The cbse improvement exam may be scheduled in the month of September from 2nd or 3rd week. You have to apply to your school if you are a regular student then the school will send you the schedule for improvement test. You can check the official site of cbse or you can check the following link to get more information.
https://news.careers360.com/cbse-class-12-improvement-exams-be-held-in-september-2020-check-details/amp
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