Hello
If you are talking about improvement exam so I am recalling you that the improvement examination you can give in the respective year when you passed your class 10 + 2 then after you will not be eligible to apply for improvement examination and if you are talking about compartment examination then you you still need to give this exam in a respective year else you will have to do your class again.
for other query you can ask in the comment section with proper keywords.
Best of luck.