Hi Harshita!

It is not possible as once student is registered in any board (CBSE/ICSE/any other state board) then he or she cannot appear in 12th class again. However, students can appear in any specific exam again for improvement in marks , but this option is limited only for 1 year after completing 12th class. Moreover, if you have not been able to get into any of the NITs with 2019 (2 attemps), 2020 (2 attempts) and 2021 (4 attempts), then I would suggest you to get into any other good private college or you can write their entrance exams. But it would a total waste of time if you keep trying for another next 3 years, also it might cause problem when you would be looking for a job as you will have atleast 6 years gap which most of the companies do not accept.

Hope I answered your query, thankyou!