Preheat the air fryer to 390°F for 3 minutes if the appliance manual recommends preheating.
Scrub the sweet potatoes under running water, dry them completely and trim any long root fibers.
Pierce each potato 5 or 6 times with a fork. Rub with oil and optional salt.
Place the potatoes in one layer with space for air to circulate. Do not wrap them in foil.
Cook 35 to 50 minutes, turning after 25 minutes. Begin checking 6- to 8-ounce potatoes at 32 minutes and very large potatoes later.
A skewer should slide through the thickest center with almost no resistance. Rest 5 minutes, split carefully and add toppings.