dear manasi,

here I am giving you the minimum marks of 12th for eligibility-

for general -50% in 12th and also 50%marks in PCB each.

for st/sc/obc-40% in12th and 40% marks in PCB each.

so if you fulfil this educational qualification condition then you are eligible for neet ug 2020.

On other hand if you want to give improvement exam of 12th standard for improve your marks in 12th then you need to go to your respective school or college .they will provide the correct information regarding this because different board have different procedure for improvement exam.