https://forums.garmin.com/archive/index.php/t-145563.html
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taken from the FR920xt manual:
Resetting the Device
If the device stops responding, you may need to reset it.
This does not erase any of your data or settings.
1 Hold “powerbutton” for 15 seconds. The device turns off.
2 Hold “powerbutton” for one second to turn on the device.
Clearing User Data
You can restore all of the device settings to the factory default values. NOTE:
This deletes all user-entered information, but it does not delete your history. 1 Hold “powerbutton”.
2 Select Yes to turn off the device.
3 While holding “downbutton” hold “powerbutton” to turn on the device. 4 Select Yes.
Restoring All Default Settings
NOTE:
This deletes all user-entered information and activity history. You can reset all settings back to the factory default values. Select “3dotbutton” > Settings > System > Restore Defaults > Yes.
Viewing Device Information
You can view the unit ID, software version, GPS version, and software information.
Select “3dotbutton” > Settings > System > About.
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