The key step to reheating nachos is to remove all the cold ingredients, like lettuce, sour cream, guacamole, and salsa, while leaving the rest to get warmed up. To reheat your nachos in an oven, preheat the oven to 300 degrees Fahrenheit — or 250 if the nachos have beans, so they don’t dry out — cover with aluminum foil and bake for up to 15 minutes.