Spray the bottom of the air fryer basket with a non-stick cooking spray.
Put frozen salmon fillets in the air fryer basket.
Set the air fryer to 400F for 5 minutes.
When the air fryer is done cooking, sprinkle the salmon fillets with salt, pepper and garlic powder. Divide butter into 2 pieces and put a piece of butter on top of each salmon fillet.
Set the air fryer to 400F for 3 minutes.
When the air fryer is done cooking, check the thickest part of the salmon to see if it's cooked enough to your liking. The exact cooking time depends on how thick is the salmon, and it's better to undercook and add more cooking time then to overcook and dry it out :) If it's not cooked enough, return it to the air fryer for an additional 3 minutes at 400F, then check again.
When the salmon is cooked through, remove it to a plate and serve.