They can be reheated in the oven, deep fryer, or air fryer. Bake hot in a 425°F oven for 5-10 minutes, flipping halfway through cook time. To deep-fry, bring 2 quarts of oil to 300°F and re-fry for just a few minutes. To air fry, set the fryer to 375°F and cook the French fries for 3-5 minutes.