If reheating in the oven, preheat an oven to 300F. Put the frozen meatballs on a baking dish or baking sheet, arranging them in a single layer. Cover the baking dish or sheet with foil and heat in the oven for about 15 minutes, or until warmed through.
If reheating on the stovetop, thaw overnight in the fridge. Put the meatballs on a nonstick skillet and heat over very low heat covered until warmed through, turning the balls a couple of times during reheating.