Betta shows are about breeding. You can't show a betta you didn't breed yourself, and learning to breed bettas and set everything up takes a lot of time, money, knowledge... and emotional strength, since you'll have quite a few failures and run into problems like your male and female attacking each other instead of mating, the male eating all the eggs, etc. It isn't for the faint of heart, or the beginner.
That said, warm, clean water and a low-stress environment will help his fins grow back. Make sure you do enough water changes for your tank, that you're regulating its temperature so it's about 77-81 degrees consistently, and that you don't have any sharp or rough decorations in the tank where he could tear his fins.
It also helps if you make sure he has a place to hide in his tank, and that he can't see his own reflection in the glass. For instance, if you leave his tank light on at night when all your other lights are off, his tank walls will turn into a one-way mirror and he'll think there's another fish threatening him all night! That can cause him to bite his fins out of stress and frustration.
If none of those things are the problem, he might just be bored and want your attention, or some plants to play in or something. If boredom is your problem, I suggest some nice live plants and maybe a snail buddy. The fish in my avatar is an on-and-off fin biter, but he seems to have stopped since I added a snail to keep him company.