To reheat a quiche, preheat the oven to 175°C(350 °F), place the quiche on a baking sheet cover with parchment paper, and bake for about 10-15 minutes, or until warmed through. I recommend to cover it with foil to avoid the quiche to turn black.  Alternatively, you can reheat quiche in the microwave for a quicker option, but the crust may become soggy. My tip if you choose this quick option is to still place it afterwards 5 minutes under the broiler of your oven or in the air fryer.