I took some pictures, this really is easy.
Filled my 2015 GSW for first time this evening and was surprised and confused by the widget in the filler. Haven't needed one on past and other TDI or any other diesel...
Makes sense to be able to use whatever filler the station has, sometimes the big truck pumps is all there is.
The instructions above are correct. Use a pair of pointy pliers in the 2 little round holes and turn the thing about 1/8 turn counterclockwise, it kind of clicks and frees up. With the same pliers or a bent pick fish the thing out, it may need to come out sideways.
Next fish the second part out, the one with trap door. If mine needed turning any to unlatch it was extra easy. Fish it out with a couple hooked picks or whatever works for you. Hard to grab onto it but once you do it is not hard to remove.
Pictures are before, the innards, and after.