To send the newly created Custom Map to a Garmin Edge it must be saved to the device. To do this, right click the custom map in the Places section on sidebar on the left-hand of Google Earth, then select Save Place As and save the file in the KMZ format.
Now move or copy the KMZ file to your Garmin handheld device in the /Garmin/CustomMaps/ directory. Alternately, the file can be saved to a microSD card, in a /Garmin/CustomMaps/ directory. Once the Custom Map is saved to the device, it will appear on your Garmin Edge by default.
While I have searched my Garmin Edge manual, I can’t find the instructions on how to create a Custom Map. However, while not specific to the Edge the following can be used as a guide: