It depends on how high a level your bishop is as to whether he can uncurse an item. Your best bet is going back to a save before equipping it and leaving it unequipped until you level the bishop up. Then save and equip it and see if he can uncurse it yet. If not, reload the save and wait some more. 
If you don't have an older save, the only other thing you can do is to put a HP regen item or two on your Lord to counteract the HP loss and wait for a level-up or two.