If you want to go for the ISRO then you need to get either a BTech/MTech/MS courses in the required field. Now ISRO works in a large spectra of cases, but the most recruitments are done on the fields provided below:

• MS in aerospace and mechanical engineering
• MS in space engineering
• MSin space and engineering systems
• MS in aerospace Propulsion
• MSin aerospace  control engineering
• MS in space and aeronautical engineering
• MS in astronautics and space engineering
• MTech/MS in Propulsion Engineering
• MTech/MS in Aerostructure Designing
• MTech/MS in Optoelectronics

To know more about Aerospace Engineering visit the link below:

https://www.careers360.com/courses/aerospace-engineering-course

I hope this answer helps. All the very best for your future endeavors!