Hi

You can appear in GATE for admission to M.Tech programme for Aerospace engineering.

All you need to do is to appear in GATE, look for eligibility in different institutions because not all institutions give M.Tech admission in Aerospace engineering as their eligibility criteria varies.

You must apply in IIST for Aerospace engineering. They offer M.Tech admission on the basis of GATE scores.

Check about both from the links given below:

GATE 2018

IIST M.Tech admission 2017