If you are not on the home screen of the app, please navigate there using the button on the top-left corner of the screen, or by tapping the back button of your device. If you are on the "Choose Playground" screen, you can sign out by tapping on the "Sign Out" button at the bottom of the screen.
Once you are on the home screen, tap the button on the top-left corner of the screen to open the menu
Tap on the " Settings" button on the bottom-left corner of the menu