Remove chicken from refrigerator 10-15 minutes before reheating to reduce temperature differential.
Preheat air fryer to 350°F (176°C) for 3-5 minutes.
Lightly spray chicken breast with oil on both sides to create a moisture barrier.
Place chicken breasts in air fryer basket with at least 1/2 inch spacing between pieces.
For whole chicken breasts, cook at 350°F for 5-7 minutes total, flipping halfway through.
For sliced chicken, cook at 350°F for 3-4 minutes total, flipping halfway through.
Check internal temperature with digital thermometer. Must reach 165°F (74°C) minimum for food safety.
Allow chicken to rest for 1-2 minutes before serving to redistribute internal moisture.