sir releavant answer de

sameerkumarsingh.ceco In your question you asked what can you do if you are going to appear again for board examination so I gave you board exam preparation tips to perform well In your question .

Nevertheless, there's no percentage barrier to be eligible for JEE mains .
To be eligible for JEE mains 2020 for BE or Btech you just need to be either appearing for 12th board exam in 2021 or should have passed it in 2020 or 2019 with Physics, mathematical and anyone of Chemistry or Biology or Biotechnology or Technical Vocational Subject.
So , even with 70% in your boards you are eligible for JEE MAINS

The only thing is that you won't be able to take admission in NITs, IIITs, IITs, GFTIs as to be eligible for these, one needs at least 75% marks in class 12 if belong to general or obc category or at least 65% marks if belongs to SC/ST or must be in the top 20 percentile in class 12 examination.

So , now that you don't have 75 % in 12th but still you want to get into NITs, IIITs, IITs, GFTIs then you can go for 12th board exam from recognised open boards like NIOS which gives you facility of on demand examination as well, so you can go for it