Speaking of food you should start feeding him some blood worms weekly this will help his diet and regrowth of his fins. I hope this could help!
I actually had been doing this for my beta Blue Bandit already [anyway], sometimes cutting his food portion, giving him a worm as a "dessert", sometimes just giving him a full worm substitution. Seems the more I give him the worms the better he looks. When I was doing the normal feeding routine as suggested by many here before, he would get better for a few days, then get worse again.
He is now near the end of his current 1 1/2 weeks of no more fin damage, and instead re-growth! xD
I think each fish is to his [or her] own, and thus you cant really follow a certain guild line for all, but instead take is as a place to start then go from there. At least that is what my little guy has proven.