Heat air fryer to 400 degrees, if preheating is recommended for your air fryer.
Thinly spread one side of each bread slice with mayonnaise. Place one slice of bread, mayonnaise side down in the air fryer basket and top with the desired amount of cheese. Top with the second slice of bread, mayonnaise side up. Cook until the sandwich is golden and crusty all over and the cheese is melted, about 3 minutes per side.