To reboot your watch press the reboot button with a pin. The reboot button in located in a small hole just above the USB charging port.  Once you press the button, power on the watch by holding the SOS button for about 3 seconds.  It may take a few minutes for the watch to find the mobile signal if you are indoors or you may need to be at a window or outside for the watch to pick up the signal.  You will not lose any information or settings by pressing the reboot button.