How to make an E.O.T for a Baseline when you are on the middle of the project and you do not have a monthly update before?

if you have approved baseline schedule, use the impacted as planned schedule analysis method because you have not an interval update 

in addition to the above mentioned, you can use the breakdown of affected activities (duration of activity) and apply it on days of delay. other way as cost wise as per BOQ

I agree with Mr. Maamoun, the solution is to use impacted as planned technique, you won't need schedule update.