Glad you asked...
The best way to reheat crab legs is in the oven. Preheat the oven for two hundred degrees. Once the oven is preheated put the crab legs on a cookie sheet for ten minutes or until they are hot.
Then again, this answer might help you...
To reheat crab legs by steaming them, is really easy. Fill a pot up with water and bring to a boil. Place a colander or a vegetable strainer over the pot and lay the legs in it. Steam for about five to seven minutes.

