I cannot remove a device from Garmin Connect that I no longer have. A 'long press' on the offending device does nothing.
When you click on a device you do have, you can get to the screen which shows the three dots, which allows you to remove the device.
I've attached the screenshot of the devices and what happens when I click on the device I no longer have.
ciq.forums.garmin.com/.../1407089.png ciq.forums.garmin.com/.../1407090.png