Hello,

Firstly as you have cleared your boards exam why do you want to apply for 12 again.

This would be waste of time don't you think so !

Secondly if you want to apply here is the help for you;

Any student who wants to take admission in Nios Open school Board Registration open for 2021 April session can now apply.

The Nios Open school Board is valid in all over India & Govt. sectors.

• You should be 16 years or above.
• You should have Scan/Photocopy of 10th class passed Mark sheet
• Address Proof (Aadhar Card)/Rent Agreement (if rented)
• Caste certificate
• Original Failure/ Compartment Without Laminated Mark sheet of class 12th for TOC (Transfer of credit)

https://nios.ac.in/student-information-section/admission-procedure.aspx

Or you can refer to this link for more information!!

Hopefully this helps!!