Smoke is usually caused by a bit of food splatter on the cooking element.  You can clean the element by making a solution of 3 grams of baking powder in 100ml of water and pour it in a spray bottle.  Spray the heating element with the solution, and leave it for a couple of minutes, then wipe it clean.  Repeat if necessary.  NOTE: Ensure the airfryer is NOT plugged in when you do this and ensure the element and inside of the air fryer is dry before plugging it back in and using.  This is based on a Philips Air Fryer so consult your manufacturer’s User Manual for specific instructions for your air fryer.