Preheat the oven to 400°F (200°C)
Spread the fries in a single layer on a baking sheet
Bake for 5 to 10 minutes, flipping halfway through
Preheat an air fryer to 350°F (175°C)
Place the fries in the air fryer basket in a single layer
Heat for 3 to 5 minutes, shaking once
Heat a skillet over medium heat
Add a small amount of oil
Cook the fries for 2 to 4 minutes, stirring occasionally
Use a microwave only if necessary
Place the fries on a microwave-safe plate with a paper towel
Heat in short intervals until warm
Avoid overcrowding the fries
Serve immediately after reheating