Dear Aspirant,

It's great that you have completed your Diploma. O feel you should go for post graduate diploma course in mechanical engineering (PG Diploma) as this will help you gain more deeper knowledge in the subject also if you plan onto doing a job it will also help you get a good pay scale. There are different colleges who offer this course.

I am providing you a link which would help you get more information on the same.

https://engineering.careers360.com/colleges/list-of-pgd-in-mechanical-engineering-colleges-in-india

Hope this Helps!
Best of Luck