Hello,

NIOS (National Institute of Open Schooling) candidates are eligible to apply for NEET. But I think you have not completed your 12th from NIOS Board, and you chose Physics Chemistry Mathematics. Now, In order to appear in NEET UG exam, PCB is mandatory and you have to appear for 12th again from any other board (NIOS in your case) by choosing PCB. You cannot use your previous Certificate or Marksheet of 12th in which your Subjects were PCM. You are going to need different Certificate of 12th. Maybe you have got clarification.

To know more about NEET UG 2021, please go through this link and use this article for further reference

https://www.google.com/amp/s/medicine.careers360.com/articles/neet-application-form/amp

Good Luck.