The Service was associated to a Device Group but why does it not appear at the access page?
The individual device must have the service first as a prerequisite.
Then you can create a device group with the same service.
If the individual device do not have the service registered, the service configured at the device group would not take effect.
In case if the device has the service registered and the same is registered at the device group, then the device group policy would take precedence.
If you want the service to be recognized at the device group without having registered the service to individual device, that would be an enhancement request.
When your AWS devices are imported, those individual devices would not have the service registered.
You can goto "Devices" and do an export to get a CSV file containing the list of devices and their properties.
Then you can modify it in EXCEL to manually register the service to those devices.
Once done, you can import the CSV again and that way you can conveniently update all those individual devices.