When I want to reheat a fully cooked ham what I'll do is preheat the oven to 350 F degrees and then just place the fully cooked ham into the oven for 10 to 15 minutes which is usually long enough to heat the fully cooked ham back up to temperature.
To keep the fully cooked ham moist and juicy place the ham cut-side down in a baking pan and tent it with foil.
Just keep check on the ham to avoid overcooking the ham but usually 15 minutes is long enough to reheat the fully cooked ham up.
Or you could place the ham into an electric roaster to slowly heat the fully cooked ham back up but I mostly reheat my fully cooked hams using the preheated over and the tin foil to keep the ham moist and juicy.