Go into the Android Auto app settings, clear the data (this allows a fresh start), then connect your phone to your head unit using the original USB cable (or, i found that a Juice cable, from Asda works). Upon connection, you should be asked if the head unit password matches the one on your phone. if it does, click to begin pairing. Press the appropriate button on your head unit that brings up Android Auto. on the bottom of the HU screen, you should see a white circle - this is where you access the apps. If the current view is (as an example) Spotify, by pressing this button, you should be able to switch over to Google Maps, etc.
