Caporegime
You don’t. Ninja specifically advise against cleaning the fan/elements. The heat will take care of anything dodgy.My only concern is cleaning the AF300/400's upper bits where the fan is situated. I haven't looked at any YT dismantling guides yet but I hope it is somewhat easy to clean as mine is gathering a bit of grease etc in the first drawer. Sausages don't half make a mess!
You can actually invalidate your warranty by attempting to clean that area.