To reset your Garmin Vivoactive 3, follow these simple steps. First, press and hold the power button until a menu appears on the screen. Next, select "Settings" and then "System." Within the System menu, choose "Reset" and then "Factory Reset." The device will prompt you to confirm the action, and upon acceptance, it will erase all user data and return to its default settings. Keep in mind that this action cannot be undone, so back up any essential data beforehand. Finally, wait for the device to complete the reset process, and it will be ready to set up as if it were brand new.