Yes u can give. DON'T WORRY...read Cbse guidelines properly for those who are telling that u can't give exam again

Hi Tarun 

Improvement exams are given by those students who want to improve their marks. So you can give improvement exam only once and it is clearly mentioned in CBSE guidelines that candidate can give class 12 improvement exam in the succeeding year only after passing in that subject in class 12. 

So as per your query you have already given your improvement exam in the succeeding year(2019) after clearing your board exams in 2018, so you cannot give improvement exam again in 2020.