Hint: it's the position between the manual maximum and the manual minimum...

Thanks to the 580's instruction book I can always move into manual zoom mode. My problem is I can't get out! The instructions makes no mention, that I can find, of how to get back into Auto Zoom mode. Help

make sure you're pressing buttons while the flash is mounted to a camera with a lens attached.  And make sure the camera is turned on when you do.