can you please tell me every details about cbse improvement exam?

You didn't mention here your subject for the impovement.

The forms for improvement exam are made available from July of every year. You can download the forms from CBSE website & print and submit to their regional CBSE offices.

How to apply for CBSE Improvement Exam:

Decide in which subjects you wish to appear in the CBSE improvement Exam.

Fill the form and submit to CBSE along with exam fees.

Wait for CBSE confirmation letter to come.

Check your examination center on CBSE official website & Wait for reception of your admit card by post.