What are the different processes involved in filling out the challenging form in RGPV?

You can go to your college and request a challenge form, after which you must go to RGPV and submit them to the university office. You will need a copy of your current mark sheet as well as your principal's signature on the form. 

It's worth noting that 1 in 1000 challengers has their marks changed. It's not that you did anything wrong, but the quality of teachers who check the copies is simply inadequate. Some students only get one mark in a subject, which is literally impossible. So go ahead and challenge, but don't give up if nothing changes, and try to write more in the re-exam.