If you do not have your OBC-NCL certificate while filling out the CUET application form , you may still apply. You have the option to apply under the General (Unreserved) category. However, to receive reservation benefits, it is recommended to upload a 'Self-Declaration' in place of the certificate and provide the official document during later verification.

To apply for CUET it is not necessary to have obc non creamy layer certificate general category candidates can also apply for the same. reservation is given to those students who are financially weak to support them for education.in order to qualify for obc  category candidates parents' annual income should be less than Rs. 8 lakhs. Salary and agricultural income are not to be considered as income for calculating annual income for creamy layer status.

Further, CUET is a entry to your dream college so prepare well for the exam.to understand the exam you need to know the syllabus providing below

https://www.google.com/amp/s/university.careers360.com/articles/cucet-sample-papers/amp

Good luck!!