SpJc11;2629815; said:try lowering the temp...
That's not good advice given the fact that you don't know the current temp. The fin rot is probably caused by poor water parameters. You may want to try doing daily 25% waterchanges combined with salt until the fish either dies or comes around. You need to keep your water pristine to have any chance of this fish making it. Don't give up until the fish is actually dead.