How to cook prefilled stuffed peppers in air fryer?

Put them in and cook them until they're done. An 'air fryer' is just a small convection oven. They're not magic. Adjust temps accordingly, as you would when converting from a still oven to a convection oven and vice versa.

Try 425* on your 'air fryer.' When you can really start to smell the peppers, they're likely done. Check them with an instant-read thermometer to 155 to 165 F and you're good. I'd cook to 165+ because it brings out the taste in the pepper. You're the cook. Cook the food. The oven you choose to use is merely a tool.

One (beef) industry recipe says cook until internal temp is 160F.
They recommend 475F at 17 to 22 min in a regular oven.
Either use that temp/time or one of yours in air fryer for one sample pepper, check internal temp and taste once that’s reached.
Adjust for 2nd pepper and beyond based on the results from first one