Usually they would use both chela for offensive/defensive actions.
My suspect is that he has suffered an injury in that "non-responsive" chela, any close-up pics or vids?
Nothing much you can do except to giving him the right husbandry.
On worst scenarios, the "malfunctioned limb" would just fall off ultimately. Unless, it is obstructing his daily movements and such, you will not to need to do anything.