When I got mine in March, and for some time after, there was no on and off for dimming the mirrors. It didn't bother me, but quite a few people complained. Two updates ago it showed up in the settings screen.
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I just checked mine and the mirror control was right where you said it was. I had skipped right past it and gone to settings to the more detailed options. I just wanted to make sure i had it off since the front windows are now tinted. Thanks for the help.