I created this to replace my 2016 VW Polo's fuel cap tether after it became perished and snapped. I cannot guarantee this will fit your car but it seems like many of the VW group cars have the same snap fit ring around the fuel cap.

Some scaling may be required if your tolerances are different to mine. I printed the ring and lid in ABS-CF and the tether in flexible TPU.

The lid will have to be glued in place to trap the tether in place permanently.