Store your leftover salmon fillets in a shallow glass airtight container for up to three days in the refrigerator. If you want to freeze them, wrap each cooled fillet tightly in plastic wrap and store in a freezer bag for two months. Reheat the fillets in your air fryer basket at 300°F for four to 5 minutes until warm. Add a single teaspoon of fresh butter on top before heating to restore moisture. Watch for an off sour smell or slimy surface texture as clear signs of spoilage.