Use DELETE {{apiPath}}/environments/{{envID}}/fidoDevicesMetadata/{{fidoDeviceID}} to remove a custom FIDO device from the Global Authenticators table.

The device ID can be taken from the mdsIdentifier field for the device in the list of devices returned when you retrieve all of the device metadata in the Global Authenticators table. The ID of each device is also displayed in the Global Authenticators table in the UI (in the column Metadata ID).