All you can adjust on back wheels is shoe position in ref to drum - that affects regular braking too (assume you have drum rear brakes). So check/adjust rear shoes - jack up, emergency brake off, tighten adjusting stars til drum stops turning and then back off so they turn. Being a new VW, your's may be ok - but I wouldn't count on it. Then you can adjust the cables using the VW brake mechanism under the tunnel boot. If it is already at the end of adjustment - then you have to shorten the cables more - usually, they are just cut and looped over with a "cincher".
Some use these cable shorteners instead of doubling over with cinchers. They look nice but cable could slip inside the connector.