Yes there is a way to get into ISRO after 12th.

1- Prepare for JEE advance.

2-give the exam and secure rank under 4.5k in All INDIA.

3-Get admission into IIST(Indian Institute of space science and technology).

Which is run by ISRO itself.

4- Get good grades entire graduation.

5-Pass the exam conducted by ISRO.

Sign the contract to work for ISRO for  3 year.

Booommm now you are working for ISRO.