Now ik I'm going to be the cruelest sounding person here when I suggest this but if you have a hospital tank I would recommend placing him in there with preferably only with a few inches of water in it so he can easily still get air from the surface. Now that's not the cruel part, the cruel part comes with this next suggestion of amputating the affected limbs of the axolotl. Now yes it may be cruel but it may also save his life in the end too. Those legs of his look severely damaged beyond repair so the best course of action imo is to amputate the limbs and let him regrow new ones. Axolotls are the masters of cellular regeneration and can regrow body parts and major organs withing as little as a few weeks, so removing the limbs isn't a death sentence like most ppl would think.