That looks nasty indeed, way worse then i had in mind

It looks like there is puss underneath or something?
Does it feel hard or something?
I think it is badly infected already when i see this.

Best thing for you to do is visit a vet or send an email out to one.

We can buy those solutions at a vetinairy and specialized terrarium stores.
Bactyfec by the way may be found with aquarium supplies as well since it originates from that hobby.

Good lucj with the frog, sorry i can't say with 100% certainty what it is,
as i said it looks worse then what i had in mind.