Preheat air fryer to 400°. Pound chicken breasts with a meat mallet to 1/2-in. thickness. Cut into 1-in. wide strips., In a shallow bowl, whisk buttermilk and pepper. Place flour in a separate shallow bowl. Mix corn chips and taco seasoning in a third bowl. Dip chicken in flour to coat both sides; shake off excess. Dip in buttermilk mixture, then in corn chip mixture, patting to help coating adhere., In batches, arrange chicken in a single layer on greased tray in air-fryer basket; spritz with cooking spray. Cook until coating is golden brown and chicken is no longer pink, 7-8 minutes on each side. Repeat with remaining chicken. Serve with ranch dip or salsa.