Preheat the oven to 250°F to 300°F
Place the prime rib in a baking dish or on a wire rack over a baking sheet
Add a little beef broth or water to the pan if desired
Cover loosely with foil
Heat until warmed through, about 15 to 30 minutes depending on thickness
Check the internal temperature and stop at 120°F to 130°F for medium-rare
Let it rest for a few minutes before serving
Slice and serve immediately