CS branches are having a lot of competition these days and it is hard to get into them. Well, you have two ways to get into the CS branch at an NIT, 

1) If you have joined any other college and want to switch then, you will have to have a minimum CGPA of 9.4, only then can you try and switch.

2) By writing JEE mains, you will have to score above 200 if you need to have a chance to get the CS branch at NIT’s. 

Good Luck.