Before getting an air fryer, I'd put it in the oven or on a frying pan. I have a pizza stone always in my oven, not just for pizza but because it reheats pizza really well. For a pan, I'd heat the pan up, toss the pizza onto it and let it sit for like 3-4mins, and then cover the pan for the last ~1-2 mins. Used to work pretty well to get a good crispy bottom crust, only downside is you'd usually get that rock hard spongey crust with this method.
Since getting an air fryer, air fryer on 350 for like 3-4 mins. Basically reheats it perfectly.