Urgent Fins Look Burned After Heater Malfunction

I am in urgent need of help. I just returned home from vacation to find that my heater in my 2 gallon betta tank malfunctioned and put the tank at 90+ degrees. I have unplugged and removed the heater and done a 20% water change with room temp water. My betta, Charles, appears to be as active as usual but the ends of his fins look like they have been burned. Is there anything I can do to help him?

 

Can you post a photo?

 

Here's the best I could take. (He's always a little camera shy.)

Here's another photo

 

I don’t think a high ambient water temp could have burned his fins, but he may have gotten a bacterial infection as a result of the stress. Are the there any other fish in the tank (aka aggression)? As long as the fins don’t get worse or turn red or white at the edge, he should be okay. Just make sure his tank stays at a stable temp in the high/mid 70s Fahrenheit.

 

I've been doing water changes and replaced the old heater with this one ( which I've used in the past) :
Betta is already improving, and I'm not seeing any signs of infection.