Couscous is best reheated in the same way you would reheat rice. Sprinkle it with a few tablespoons of water, microwave until warm steamy then fluff with a fork to break up any clumps. If you don't have a microwave you can add the couscous to a saucepan, along with a splash of water. Cover the pan with a tight-fitting lid and cook over low heat, stirring occasionally, until heated through.