You could also reheat fries on the stove, in some oil. You can reheat them in a frying pan with no oil and do a dry fry or you can put them in a deep fry. The problem with the deep fry is that it makes the fries extra oily. Now, you can wipe off some of the oil once they come out, using a paper towel, but they will still have absorbed quite a bit of oil. Deep frying French fries to reheat them is not the healthiest way to warm them up.
To fry in oil, just preheat the oil on medium heat and cook for about three minutes. It doesn’t take long to warm them up in hot oil.
Dry frying works okay, but you need to let the fries reach room temperature first before putting them in the frying pan. Then, heat them on a low heat setting to warm them slowly, so they heat all the way through.
For dry frying, it should take about five minutes to warm the fries enough that they will be warm all the way through.