If the exit button is not available in the bottom menu, chances are you set DMD² as your device default home app.

The default home launcher is the app which is shown when your device first starts or when you press the home button.

Some users want their devices to behave more like a traditional Android device, with a regular or stock launcher where they can launch any app including DMD². Other users will use the tablet mostly on their motorcycles and want DMD² to be the default home app. For this reason DMD² can be setup as the default home app or you can use it as a regular app.

Whatever you prefer, notice that you can always change this at any time. The default home app is an Android setting that can be changed in the Android settings.