Preheat the air-fryer to 400 F. Cut string cheese sticks into small bites. Whisk egg and milk together in a shallow dish. Place flour into another dish.
Combine breadcrumbs and seasoning in another dish. Dip each mozzarella bite into the egg, coat in flour, dip back into the egg, and fully coat in the breadcrumb mixture.
Set onto plates. Freeze for at least one hour. Air-fry in batches for 8-10 minutes.