How to reheat a baked potato?
Sadly, baked potatoes are one of those foods that are only truly at their peak when first baked. Either re-baking them or microwaving them will give the least bad results for reheating.
Your better bet, however, is to give them a new life, for example as potato pancakes, hash browns, as an ingredient in a hash, or similar application. While they won't have the same quality as a fresh baked potato, these can be very good dishes.