Cracked tongue on our nali

[Mexican cuties]

. Our nali has always had his tongue out due to a naff jaw, but his tongue has a raised almost blistered patch on his tongue, saw our vets and advised to keep dropping water onto it to keep it as moist as possible, not much difference and he does not seem to be drinking as much so we are keeping an eye on it, saw on a website that advised a drop of olive oil would help or frozen chicken stock cubes, any other suggestions, he's back at vets today for his allergy jabs so will see what the vet says.

Many thanks