Preheat the oven to 400°F
Spread the fries in a single layer on a baking sheet
Bake for 5 to 10 minutes
Flip the fries halfway through
Remove when hot and crisp
Use an air fryer at 350°F for 3 to 5 minutes
Heat a skillet over medium heat
Add a small amount of oil
Cook the fries, stirring occasionally, until warmed through
Avoid microwaving if you want them crispy