I'm not sure, but try to use the following procedure:

1. Power on the chartplotter
2. As soon as 'Garmin' appears, press and hold the Upper Left corner of the screen until the message 'Do you really want to erase all user settings?' appears
3. Choose 'Yes'

NOTE! Pre-save your user data (waypoints, routes, Auto Guidance paths, tracks, and boundaries) to an SD card since after such a reset all this data will be erased.