Hi!

ISRO selects Scientists , in the following steps:

1. ISRO recruits some freshers in campus drive from some IITs and NITs.
2. Complete B.E./B. Tech from any other AICTE approved college in India, give ICRB's exam for Scientist/Engineer for your stream, clear the interview and get into ISRO.

However you can only become a scientist after completing your graduation degree.

Best of Luck.