Break the graham cracker sheets in half so that you have 4 squares.
Place 2 graham cracker halves in the base of an air fryer. Cut or tear off ¼-inch from the bottom of 2 marshmallows to expose the sticky interior. Place the sticky side of the marshmallows on the graham cracker halves (this helps the marshmallow from flying off the graham cracker in the air fryer.) Air fry at 350°F for 2 to 3 minutes.
Place the other two graham cracker halves in the air fryer. Top each with ½ of the chocolate bars (stack the chocolate if needed). Air fry at 350°F for 1 more minute.
With a small spatula, carefully remove the graham crackers from the air fryer. Press the chocolate side of one graham cracker over top of the marshmallow. Let rest for 1 to 2 minutes before eating (the marshmallow will be very hot!)
Notes
If you prefer chocolate that is less melty, you can just air fry the marshmallow half, press the piece of chocolate on top of the soft marshmallow, then top it with another graham cracker, and enjoy.
Cooking time will depend on your air fryer, so check the marshmallows after 2 minutes. Continue air frying if needed.
If you are making subsequent batches, and your air fryer is now pre-heated, decrease the cooking time on the marshmallow to 1 to 2 minutes so it doesn't burn.
Wait a minute or two before eating the s'mores. The marshmallows will be very hot, so give them a bit of time to cool down.