WARNING: This page is about a different car, the 2011 BMW 750xi, 2011 BMW 750Lxi, 2010 BMW 750xi, and 2010 BMW 750Lxi. However, it is still accessible from the selected car via links, so may be relevant.
Detach side wall.
Open welded connections in area (1) and remove side member cover (2).
Fig 1: Identifying Side Member Cover And Welded Connection Area