Hii..

As your query is about private candidate in CBSE .. as there are many condition or eligibility for private candidates in CBSE you have not mention here if you are passed in 2018 and why want to apply for private candidate ....

so to know about the private candidate eligibility and guidelines and about the condition where can a candidate apply for private candidates go through this link where you can clear your doubts:

http://www.cbse.nic.in/faq/private_candidate.htm

https://cbseonline.ernet.in/pvtform/

All the best!!