._______. ugh that's awful. I'm a huge animal lover so that's hard to read.
Like, in that situation the vet is the best solution no matter what, but if that's definitely out of the question then you need to assess how bad the damage is.
Is there a gaping hole? If there is he needs stitches, if not, you can probably fix this at home. You should get some wound cleaner, make sure it's digestible since the wound is around the mouth. I'm not sure if Saline solution is digestible BUT Saline solution doesn't hurt when you apply it to the area which is a HUGE plus since your dog is already in a lot of pain.
Is the wound IN the mouth? Because it should be bandaged up but the mouth is a really hard place to wrap.