First you need to have a bachelor's degree in astrophysics or physics. Currently, no Indian institute offers you a BSc degree in astrophysics so you can apply for Universities abroad like Harvard , Stanford, MIT etc. However, if you want to study in India only you can get a bachelor's degree in physics and then masters degree in astrophysics from institutes like IISC, IITs.

After completing your degree you can either go for PHD in this field or can get a job in ISRO or NASA however this might be a very tough job as the competition in this field.

Hope it helps.

Thank you.