Preheat an oven or toaster oven to 400°F
Spread the fries in a single layer on a baking sheet
Heat for 3 to 5 minutes
Flip the fries halfway through
Remove when hot and crisp
Alternatively, heat in an air fryer at 350°F for 2 to 4 minutes
Shake the basket halfway through
Avoid microwaving if you want them crispy