How can I treat my fish's mouth injury?

it seams your tank has a lot of carp in it that will grow up to be very big fish. Your tank seams like it is a little over stocked. and your fish are probably fighting. If you can you should get rid of some fish or get another tank. I hade a 3in koi and a 2in goldie and a pleco in a 20 gal and i would say that it was over stocked for that type of fish. Im not fussing im just letting you know. Add aquarium salts and stress zyme (to help heal) and rearrange any decorations you have to help with the fighting. GOOD LUCK