dear aspirant,hope you are doing well

now coming to your question,as the the latest guidelines of Cbse regarding these are some rules regarding improvement exam:

1.Cbse improvement examination is only for those students who had previously attended the board examination, and who qualified in that examination. The purpose of this examination is to give another opportunity to the students to re-score good marks, through which they can improve their result, and make themselves satisfied.

2.In improvement exams, students have the chance to give the re-exam of one or more subjects, in which he/she can score better.
This exam is only for those students who had been qualified for the class 12th board examination.

3.Those students who had appeared last year in the board exams, their details will be auto-generated, and the other students have to fill the form of the CBSE improvement exam.

4.Students who have not passed their previous year board examination are not eligible for this examination, they have to fill the compartment form to entertain this.
In many such exceptional cases like, if the student fails to score good marks in the improvement exam, then the students best performance will be considered.

5.The student who wants to give the CBSE improvement exam cannot engage or cannot pursue any of the other higher studies, he/she will not be eligible for the improvement exam, he/she should be a dropper for that current year in which he/she is pursuing the improvement exam.

hope this will help

for futher queries related to this topic,feel free to post down in the comment section below.