WARNING: This page is about a different car, the 2014 Volkswagen Touareg, 2013 Volkswagen Touareg, 2012 Volkswagen Touareg, and 2011 Volkswagen Touareg. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Installing Fuel Filler Door
Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.
-- Place the fuel filler door -1- on the fuel filler door unit -4- -arrow a-.
-- Slide the fuel filler door in the direction of -arrow b- until the retaining hooks -2 and 3- engage with one another.