Hi aspirant,
The eligibility criteria for dropper is -For NITs,
admissions, the candidates should have obtained a minimum of 75% aggregate marks or be in the top 20 percentile of their respective boards. For SC/ST category, a minimum of 65% marks required. If the candidate appears for improvement in 2020, then the top 20 percentile of 2019 will be taken into account. The maximum marks secured in the necessary subjects will be considered to calculate the aggregate percentage in such a case. The marks of only five main subjects is considere by NIT's. Follow this link for more details-https://www.google.com/amp/s/engineering.careers360.com/articles/jee-main-eligibility-criteria/amp
Hope this helps.