Is it possible to fill the JEE mains for if take admission in NIT this year?

You are not going to get admission in any NIT without JEE marks, If u already taken admission in some NIT on the basis of JEE marks but u are not satisfied with that, ofcouse you can appear for JEE next year. But if u are look for admission in some other good institute the best options are BITS Pila

Yes u can fill form next year