Had a quick look through this thread a while ago and didn't recall seeing any pics so I thought while I did mine finally the other day I might take a few for the newbies too see and also do it a different way from the others.
This is in the off position, the the left of the circle is the auto position
With a small flat blade screw driver insert it carefully at the base of the light switch knob and pop it off the light switch shaft
This 2nd plastic stop is all that is stopping the light switch knob from rotating around into the auto position, I have read else where that people remove this with tools such as dremels, die grinders, swiss army knives and even nail cutters LOL, I am not a fan of butchering my light switch assy so I thought of an different way to do mine
I decided to cut away the excess plastic off the back of the light switch knob instead with just a small stanley knife, I cut about half of it away as you can see in the two pics below
Push the light switch knob back onto your light switch and now rotate past the off circle to the auto position, only thing you will need now is a letter A sticker to put on there, going to try and see if a local newsagent has a set next time I take it out for a lap
If your unsure of anything please ask and I will try to help