Usually it can be worn down by feeding them food whole so they have to tear at it, by feeding them on a piece of stone or slate and by providing cuttle bone to chew on.
Unless it is very overgrown, intervention isn't usually needed.
Depends on how overgrown it is. If it is only slightly overgrown you can wear it down naturally, abrasive food plates, cuttle bone and the like. If on the other hand his nickname is dumbo the elephant and it interferes with eating, then a nail trimmer or dremel can be used to do it.