Ouh... I know what that is. That's bacterial. Frequent big waterchanges, fresh catappa leaves and alder cones. All you can do. But as it's on the mouth and the upper jaw is basically gone I see little chance of survival even if it should be cured of the infection. I would euthanize.
Here in the EU we also have little to no meds. Antibiotics are only available via a vet, imo a good thing, because we have enough multiresistant bacteria strains in aquaria. Otherwise we only have a limited number of working active ingredients, limiting the number of treatable things, too. The worst thing in the past years was the prohibition of almost all actually effective worm medications against gill flukes and tapeworm.
But honestly, many things are best treated without meds and nothing beats optimal conditions and regular waterchanges.