Would someone please tell me the best way to reheat mashed potatoes if you don't have a microwave oven?

They are left over from a couple nights ago and I plan on making some gravy to go over the top along with chicken,onion, garlic, an bell pepper that needs to be used up.

I am trying to use up leftovers and food before it goes bad. I thought about putting the potatoes in a pan on the stove on low but have to add milk? or in the oven and what temp?

This is for dinner tonight so please help soon! Thanks