Butter one side of 4 pieces of bread. Lay with butter side down on air fryer rack or basket. (if you have a small machine you may only be able to do one at a time)
Sprinkle cheeses on non buttered side, then lay 2nd piece of buttered bread with butter side facing up on to your sandwich and close your basket.
Cook for 4-6 minutes depending on how thick your cheese is. After 1 minute, open basket and check as top piece may have blown off. If it did put back on and press in center to make it stick with melted cheese in middle.
Also timing will vary according to amount of cheese and other added ingredients you include inside, and how large your bread slices are.