HELLO,

Yes you can appear in the improvement exam in the same year to increase your marks even if you have already passed your 12th standard exams. However there may be some limitations and rules depending on the education board ( Like CBSE) and whether you are appearing as regular or private candidate

HERE ARE SOME MORE NECESSARY DETAILS YOU SHOULD KNOW:-

1.Most boards allow students to give the improvement exam in one or two subjects to improve their scores

2.In the CBSE system you can appear for improvement exams in the same year or the succeeding year as a private candidate

3.Conditions are that you must have passed the subject in the previous exam to be eligible for improvement

4.There might be limits on the attempts like only once in the same year but you can appear in subsequent years

So it is important to check the specific board rules and regulations like exact eligibility criteria and application process before giving the improvement exam

Hope this Helps!