WARNING: This page is about a different car, the 2010 BMW M3, 2009 BMW M3, and 2008 BMW M3. However, it is still accessible from the selected car via links, so may be relevant.
Open door window.
Fit special tool 51 0 320 in front door and press back as far as it will go.
NOTE:
Special tool 51 0 320 must rest against door and reach the stop on guide (1).