WARNING: This page is about a different car, the 2013 BMW X5 M, 2012 BMW X5 M, 2011 BMW X5 M, and 2010 BMW X5 M. However, it is still accessible from the selected car via links, so may be relevant.
Mark new part (rear wheel arch outer half) in accordance with severance cut on vehicle + 20 mm extra material and cut (1).
Weld new part in area (2) overlapping.
Fig 1: Identifying Severance Cut And Welded Joints Area