Growth on betta?

[Cocoa19]

Hey guys so today I bought a Half moon Mascot betta and we all noticed he had a growth on his tail, he seems fine otherwise but I just wanted to know if anyone knows what it is or if I can somehow remove it? if not that's fine just don't want it to get bigger and it start to affect him. pictures below sorry it's hard to see but the growth does actually go through both sides, white dot in 2nd photo is part of it (photos are of him at store he is now in a 21L tank)