Reheat refrigerated fajita filling in the microwave or in a skillet until desired temperature. Do the same for the tortillas and then assemble. Feel free to use an air fryer to reheat both at the same time—350 degrees for 3-5 minutes or until it's warmed to your liking. If using frozen ingredients, you can thaw the veggies and tortillas overnight in the fridge or slowly heat in a skillet over medium low heat.