Hii aspirant..

The Official website says  -

A candidate who has passed Class 10th / 12th exams but would like to go for Improvement exam to improve performance in one or more subjects can reappear in the main examination in the succeeding year only. If you have passed class 10th / 12th this year, you have to wait for next year main examination.

For subjects involving practical work, in case the candidate has passed in practical at the main examination, he/she shall be allowed to appear in the theory part only and marks in practical obtained at the main examination shall be carried forward and accounted for.

In case a candidate has failed in practical he/she shall have to appear in theory and practical both irrespective of the fact that he/she has already cleared the theory examination.

Hope this helps. 

Best of luck.