See you can only join a 3 year BTech program if and only if you have completed a Diploma course in Engineering. If you are such student, then you have to sit for the lateral entry examination for engineering BTech. Now the examination which you can give being a student of Andhra Pradesh then you have to qualify the AP ECET examination. By qualifying this examination, if you take admission in the BTech courses then you will be provided direct admission to the 2nd year of BTech.

To know more about AP ECET visit the link below:

https://engineering.careers360.com/articles/ap-ecet

I hope this answer helps. All the very best for your future endeavors!