Preheat the oven to 350°F
Place the apple pie on a baking sheet
Cover the crust loosely with foil if needed
Heat for 15 to 20 minutes
Remove the foil for the last 5 minutes if you want a crisp crust
Check that the filling is hot before serving
Let the pie cool for a few minutes before slicing
Reheat individual slices in the microwave for 20 to 30 seconds if needed
Reheat slices in an oven or toaster oven for a better crust