Diploma students who have completed their degree, or are in the final year of doing so, are eligible to apply for JEE Main , but will not be given admission to NITs and CFTIs. If you qualify JEE Main, you will have to appear for JEE Advanced, and they will be given admission like class 12th pass students. No lateral entry.

You can also refer the link given below. There you will get more information regarding this

https://www.careers360.com/question-can-a-diploma-holder-without-class-12-apply-for-jee-mains-of-so-than-how-plz-tell