Actually Astrophysics course is not so popular in India. It is still a niche course but with great potential. It is not like any course which is being offered by any particular college but overall a mixture of Physics and Maths with Astronomy.

You must excel in physics and mathematics in your high School especially 11th and 12th as it will build your foundation.

Graduate with either a BTech degree or a BSc degree in any domain that you're interested in from a reputed college. Doing it in either a science or mathematics field would prove to be extremely useful. You can even do internship in NCRAA, IUCAA, Vigyan Prasar for further knowledge.

You might go for a BSc. or BS-MS in Physics and then complete your Ph.D. in Astrophysics. IISc, IISERs and IITs like IIT Kanpur are really good institutes for a degree in Physics.

All the best!!