Play Store updates only work when DMD2 was installed from the Play Store.

There are two ways to get DMD2 and they update by different routes:

• Google Play — the route for any device that has the Play Store. Updates arrive through Play like any other app. This build has no in-app updater and no App Update row in Settings, because Play does not allow an app to update itself from outside the store.
• Sideloaded APK — the route for DMD Navigation units and anything else without the Play Store. This build checks for new releases itself and prompts you to update in place.

If your device is a DMD Navigation unit, or you installed the APK yourself, you have the second one. Take the in-app update when it appears, do not go looking in the Play Store, and do not worry that Play shows nothing.

You cannot simply move from one route to the other. Both builds share a package name but are signed with different keys, so Android will not install one over the other. Switching means uninstalling first, and that clears the app's data. If you must do it, sign in to the DMD HUB and let a sync finish beforehand, and expect to download your offline maps again.

Both routes are described on the app download page.