Talk to General Physician on Thumb Sucking Callus

AoA, my brother who has just turned 15 finally decided to quit thumb sucking last year. The issue now is the callus that has formed on his thumb. It's placed right on the lower part of his thumb. My parents have checked up on him a few times at night to make sure he's not doing it in his sleep and apparently he has quit for sure. The issue here is that he does not want to see a dermatologist or anyone for that matter to have it fixed. His teeth are seemingly normal and so is his jaw. My parents would like to know if there is any sort of remedy or ointment that they could apply on his thumb to have the callus fadeaway. We'll be super grateful if anyone here can help us out. Thanks!