The current MSFS Navigraph Navdata has a separate installer and does not use the FMS Data Manager.
You download the Navigraph MSFS Navdata Update installer from Navigraph Navdata Center
The installer takes about a minute and places the Navigraph Navdata Update into MSFS ready for load next time you run MSFS, which will take a little longer first run. The installer then shows a Remove button should you wish to remove the beta data.
To check if the Navigraph Navdata Center is installed, please see FAQ - Is the Navigraph Navdata for MSFS Installed?