Hello,

NIOS is national institute of open schooling. You failed mathematics subject in 2020. CISCE board you are getting failed. So for NIOS you can get credit transfer maximum in 4 subject or old and new students. And if you are CBSE/ CISCE board students then you can get maximum two subjects credit transfer. So you can give only one subject examination from NIOS.

The process of registration NIOS is -
You have to visit www.nios.ac.in (NIOS WebSite) and under On-Demand Examination Click upon the Registration for Examination only for existing learners (at the bottom). After that the regulation form will appear where you have to register for the Examination.

All the best.