When it's split due to damage, it often repairs in time in good conditions. Ime, though, when there's a gap like that it's probably a genetic imperfection, just part of the specimen, and not something you can 'heal'. In some species, or at least from some parents, it seems you get a certain number of offspring that have the imperfection.
If you research it, with fin damage there's normally a window of time where certain biochemical events need to take place for regeneration. If the process begins within the window you'll probably see regeneration, if not you probably don't. That's one reason some people say this or that will heal and some people say it won't.
My impression from your photo, though, is it's genetic feature, probably not something that will 'heal'.