Instructions
Push the "Check" (the button with the check mark) and the "Start" (the button with the arrow) buttons on top of the device at the same time for about three seconds until you see the "Volume Control" menu pattern -- a red center grid tile with blue tiles bordering it.
Twist the grid counterclockwise to decrease the volume until it's completely turned off.
Press the "Check" and "Start" buttons for at least three seconds to exit the menu; or simply wait for about five seconds for your Rubik's Slide to exit the menu automatically.