Hey, 1fish2fish is correct! and I have found daily water changes, almost 100%, adding de-chlorinated water, with a pinch of aquarium salt dissolved into the water first before adding. I will feed frozen blood workms for a week or two.
Also something that speeds up my fin recovery 2-3 dyas faster is using dried, OAK LEAVES. OFL, let me know about this one, an I use them religiously!
If you have any Oak trees where you live, look for hangig dead ranches of the ground, with brown dried leaves. Use anywhere from 1-10 leaves depending on the size and type of oak tree it is. I have found White ot Bur Oak leaves to be the best!
Keep up the daily water changes and feeding for 10 days - 2 weeks and your bettas fins should be making some serious progress!
If your unsure, you can post a pic and I will let you know!
Good Luck with the repair!