Hey Udit !!

I hope you are doing well. As per your mentioned query , if you are not qualified in the jee mains exam of 2021 and after that you repeat your class 12 , so it doesn't mean that you are now qualified for the jee advanced. As per the guidelines , you have to again give the entrance exam of jee mains first and if you will pass the jee mains exam then you will be able to give the jee advanced examination.

I hope it helps.

Good luck !!