Ringo has two buttons that have the same function.
One is the power button, conveniently positioned just below the screen.
The other is a small button located on the right side of the main board, right next to the white "ON" sign.
If the phone is turned off, press and hold either of these two buttons for a few seconds until something appears on the screen.
If the phone is already on, press and hold either of the two buttons until a screen pops-up allowing you to choose between powering off or restarting your phone. Select the desired option and press the A button.