Hello aspirant

Top entrance exam for MTech Aerospace Engineering is GATE. Through GATE score you can take admission in top colleges.

For example

IIT Bombay - M.Tech Aerodynamics

IIT Madras - M.Tech Aerospace Engineering

IIT Kharagpur - M.Tech Aerospace Engineering

IIT Kanpur - M.Tech Aerospace Engineering

IISc Bangalore - M.Tech Aerospace Engineering

IIT Hyderabad - M.Tech Aerospace Engineering

For more information you can go through this

https://engineering.careers360.com/colleges/list-of-me-mtech-in-aerospace-engineering-colleges-in-india

Good luck :)