Yes, you would be able and eligible to apply for the BITSAT, even if you have given the papers for improvement.
But you should have scored a minimum 75% marks in aggregate in Physics, Chemistry and Mathematics.
Additionally, the candidate must have scored minimum 60% in each paper.
For further details, if you have any query you can even visit our website, where there is a detailed description which would be quite helpful for you.
Yes definitely you are eligible to appear for BITSAT 2019 ,But make sure to score 75% aggregate marks in PCM in improvement exam in order to become eligible for admission in BITS campuses.