Is the mold getting worse or spreading or anything?
What have you tried? Tried removing the bladder and washing the mold off? IF it will wash off, that's really the only way that comes to mind for me. Take the bladder out and clean it. Be careful though not to bust it while handling it. If it was me, I'd prolly just do nothing about it except try to store my kite drier in the future. I wouldn't even mess with it until you have a reason to remove the bladder, that is, if you ever have a reason to remove the bladder.