The current Navigraph MSFS Navdata Update Beta has a separate installer and does not use the FMS Data Manager.
You download the Navigraph MSFS Navdata Update installer from Navigraph Navdata Beta .
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 Beta installed, please see FAQ - Is the Beta Update Installed?