As reddit user Peter_73, who recently got this new feature, explains in a post, the rollout is most likely powered by a server-side switch, so there’s not much you can do right now to receive the same update on your device.
Google is the one deciding who gets it and when, so our only option is to just wait for the company to start the mass rollout for all Android Auto users.
In the meantime, you’re probably wondering why choosing the driver seat location is such an important setting for the overall experience with Android Auto.
In theory, this option makes it possible for users to choose if they want Android Auto (and all the other apps) to run in right-hand or left-hand-drive mode, with the interface therefore adapting according to their settings.
As you could easily figure out, this is very important for navigation apps in general and Google Maps in particular. Users have been complaining of various problems with the RHD layout, and now that this setting is finally going live, they will be allowed to configure how they want the navigation app to display the interface manually.
At this point, however, it’s not yet known when the general availability could be reached, as Google is most likely still in the testing phase and is just trying to collect more feedback before everybody receives the new setting. When the general availability is reached, we'll let you know when the feature goes live for everybody running Android Auto.