Garmin Customer Support to register the device using Garmin Express
In every type of device, you would need to provide your email address to register it at the time of device setup. Though there is no need to enter your personal details like name, address, number or serial number. You would only have to fill the email address.
Note: If you already have a Garmin account then make sure to use the same email address that you have used at the time of creating the account. This way, your device will appear on the list of the registered products.
For those devices which already have links with the Garmin Connect; automatically these devices will get register during the setup of the device. In addition, it will display the registered device on the linking Garmin Connect Account during the device setup.

If you come across with any kind of trouble at the time of linking the account or during the registration then you would need Garmin Tech Support. Therefore, for proper guidance, visit the website.
