How to answer boldly in interview? because when interviewer ask any question after that my heart beat going to high level and totally black out.

Look into their eyes confidently even if you don't know the answer. The confidence you will gain eventually slows down your heart beat. You will be able to analyse the question there onwards. Do not wander your stare anywhere, but only into their eyes. A stare without blinks will gain you all the confidence that you think you won't have till you enter the room.

I think before you enter an interview meeting, take the following step:

Take two deep breath.

Believe in your gut, no matter what; that you are good

Assume that the interviewer or interviewers are your friends or colleagues; so you won't have to panic

Answer in your mind and then open your mouth and talk.

You can smile to gain some seconds and consciousness from the blackout before you answer the question.

Those are the strategies I often use.

The way to overcome this is by understanding why you're feeling anxiety in the first place. First, don't think you're alone in this - we are all human and we all feel anxiety going into interviews. However, the level of anxiety each of us feels is equivalent to the level of confidence we have prior to going into the interview. 

The steps I use to overcome this are:

1) Envision the interview before it happens with a POSITIVE outcome in your head. Do this over and over and over. Every time you do this you'll lay another building block of confidence in your mind.

2) Repetition. Keep going to those interviews and keep doing your best. You're going to have a good interview and feel great afterwards. Just keep a positive attitude and you'll have more good interviews and those will equal more confidence until you don't feel anxious about them anymore. 

3) Research the company and the position you're interviewing for. Keep in mind that you're already a fit for that position or they wouldn't be interviewing you in the first place. They already see something positive in you. Realize this beforehand and sell yourself on your strong points. 

You just have to sit down with yourself and focus on the reasoning behind why you feel so anxious in the first place. I've interviewed literally hundreds of applicants for various jobs and nearly everyone has been anxious. It's normal my friend. Just use the basic building blocks to more confidence and you'll overcome it. This I assure you. If you need more tips or advice then send me a message. I'll help you.