Hi,

It is not necessary for students who have completed their diploma to appear for JEE Mains. If you take admission on the basis of JEE Mains, you will have to start your B.tech from the first year. Else, there are many colleges that offer lateral entries in 2nd year B.tech for those who have completed their diploma. Lateral entries can be on the basis of entrance exams conducted by the colleges or on the basis of merit.

I hope this helped you.