As per  JOSSA eligibility for JEE Main you should have secured above the cutoff rank in JEE Main 2018 Paper I, For the admissions into NITs, IIITs and GFTIs, the general candidates should have scored 75% and OBC-NCL/ SC/ ST/ PwD candidates should have secured 65%. You can check the complete eligibility with the given below link.

JOSSA Eligibility 2018

Good Luck!