What do you think are the key things to control one's nervousness while conducting a training session with High Officials?

There have been good recommendations by our colleagues, so will not repeat them.
I have couple of comments.
First of all, I think a teacher/trainer has to know his/her audience and talk to them "in their own language".
That means the teacher/trainer should have various styles and methods of teaching and he/she should choose (sometimes modify) the one that best suits.
There is no recipe to suit all .
Once you are confident in your knowledge of the subject, you must have a feeling that you know more than anyone in the room on the subject being taught and there is no reason for nervousness.
The most important factor to avoid the nervousness is KNOWLEDGE of the subject and geniune DESIRE to pass this knowledge to the trainees!

Most important is :To know your audience well.
The more confident you are that you are presenting them with useful and interesting material for them, the less nervous you will be overall.
With high officials- little interaction with the representatives of audience as to what they expect from the training.
(Pre training- through mails)-Intimating few representatives about the agenda & asking for any missing contents/ suggestions to be added & suggestions on questions which the target audience expects to be answered while training Greet members on their entry & striking an introductory conversation of few minutes with them just to brief them about the objectives While delivering training- it is also very important to know your material well.You also need to structure your session by prioritizing certain keywords/phrases in your mind on which you need to elaborate & explain.
Practice & prepare-just before the session give it a final run through Calm yourself- practice deep breathing, drink water, smile & relax

From the beginning and before answering, why should you be nervous while conducting the training session? Prior the training session if you are nervous conducting it you should not attend and delegate it to someone else that has a control on his attitude and emotions.
The term "High Officials" is broad and varies depending on the type of officiality; in such government officials or organization officials.
The only case that should make someone nervous during a training session is to have something personal or directed as personal in a way of humiliation, deep impressing and harassments, and it can be avoided by the way of the trainer in the session.
If the trainer is professional he/she will remain focused on the subject and not to deviate from the required target/s to be delivered.
And if it reached a point of nervousness as you mentioned and I don't know why, a break will cut the situation imposed or a subject change /shift to next point in the course should be sufficient.
Knowing that any difference in the opinions is still not personal and it is still business, and business is business.
This answer is based on the "nervousness" meaning in the question unless it is meant in a different way.
Hope that satisfies your query.
Kind regards.

1 – Know Your Audience 2 – Know Your Material 3 – Structure Your Presentation 4 – Practice, Practice, Practice 5 – Prepare, Prepare, Prepare 6 – Calm Yourself from the Inside

Great question Nervous is not always a question of getting ready with your training material .
What is nervous and reasons let us think about it and feel it to get ready to deal with it .
first moment of silent and thinking of what you should say.
nervous comes to your mind when you see their eyes staring at you in the first silent moments .then you will get more nervous when your words comes unstructured , and see their eyes discovering you , you will be surrounded by these staring eyes , smiled teeth .
then when the first smile comes from that person setting at that table you are totally shay unable to control red cheek , then you find your eyes directed toward that uninterested person , you are unstable can't concentrate .they now begin to change their setting position in more comfortable , crossed legs , crossed arms.
you miss your first impression.
Any professional trainer lied to you if he told that he didn’t come onto this situation when he was beginner .
When I coatched new hired trainers, I felt one day of what they feel now ,it is time to give a hand to them .
so what should you do ? 1-Control your breath .

2- Don’t talk so fast or so laud this will make your mouth more dried .
and unable to continue.

3- smile and don’t reveal these feelings of uncomfortably .
you are in the moment of truth so reveal that you hold the horse bridle.
4-fist moment of trainee are exploratory stage of you , it is so critical moment of first impression , if you were confused & forgot what you should say , you should Start your session getting to know them but in a way that you can make them involved through driving them to talk about themselves in a way that you initiate asking and discussion.
No trainer can success as a one man show .

5- their eyes that were frighten you are controlled by you , you are directing them to the person that you are asking and responding .
it is so easy but, you should stand In both closed crossed hands, high chest , shoulders , raise your head with smile that permits normal breath , ask the next person to introduce himself .
walk to the next with greeting .

6- you are now walking across , holding their attention and talk .

7- now unleash the giant inside you .

8- move confidently , introduce the topic , trigger them to define the first title .

9- now you are comfortable unaware of your nervous .
Don’t forget .
that it is normal.
And you can do it .
best regards Abdullah obiedat

Before the training, instead of thinking too much on how to answer their questions, try to relax and think of happy thoughts or the times you've made successful trainings, that way the nervousness will go down - worked for me.
Master your presentation and set an ample time to do your homework about your topic for training

always start your training with a fun exercise , it breaks the ice, make friendly enviroment and helps you in knowing your audience more

I would prepare few questions and keep them for such a case...!! The best way to control nervousness is to change participants attention off the trainer.
Asking questions that are related to the training course is one of the methods to get back confidence and concentration.

We can know things through our practice of student work that he loves, whether served easy or difficult and Amemknna to identify the nature of the people through dealing with them and good practice

The best thing to do is to know what you are going to talk about. HAving confidence in one's ability and being the subject matter expert always helps!

You need to ensure that you are:

• Planning and writing the presentation
• Using visual aids effectively
• Overcoming presentation nerves
• Delivering the presentation confidently
• Answering questions competently 

Hope this helps!

Cheers

Be a professional! Always remember that you are doing your job and this is what you get paid for!! Besides, senior management appreciates it better when they know they have capable hands in the organization.