Hello Aspirant !

You have to score 75% in 12th boards with the subjects Physics Chemistry Maths English and one other subject

Then , clear JEE Mains paper 1.

Then , try to get rank under 1000 in JEE Advance and submit your rank to IIST website.

You can also check the eligibility criteria and more details about IIST on our site and official site by following links :

https://www.iist.ac.in/

https://www.careers360.com/university/indian-institute-of-space-science-and-technology-thiruvananthapuram

Hope it helps !