You can reheat the burger in the oven wrapped in foil for about 10 minutes at 350 degrees F. Or place it on a plate and microwave at 50% power for 30 seconds to 1 minute, depending on the size and thickness of the hamburger. Note: Reheated hamburgers may not taste as good or have the same texture as when freshly cooked, but this method will help you enjoy a warm and tasty burger.