Mix together soy sauce, pepper, minced garlic, fresh rosemary, and olive oil in a large bowl, reserving a third of it in a separate bowl to use for basting.
Add the chicken thighs to the bowl with the larger amount of sauce, cover, and place it in the refrigerator for 15 minutes.
Allow your air fryer to preheat to 400 degrees and place the chicken thighs in the air fryer basket.
Air fry the chicken tenders for 7-8 minutes and flip them over. Use a basting brush to cover both sides of the chicken thighs with the sauce that was not used for the marinade.
Cook for an additional 7-8 minutes. Check the internal temperature of the chicken thighs to ensure it has reached 165F. Allow the chicken to rest for a few minutes before serving for optimal juiciness.
For bone-in chicken thighs, increase the cooking time to 30 minutes, flipping them halfway through. Always check for doneness with a meat thermometer. Chicken should reach an internal temperature of 165F.