From GExtension Wiki
Make these steps if you want to import players and bans from ULX or ServerGuard. You may should do that before you open your server to public.
This will only import the users with their groups (and bans), not the groups itself. You have to create the groups before (Admin -> Settings -> Groups).
Run the appropriate command in the server or client console:
- gex_import_ulib for ULX
- gex_import_serverguard for ServerGuard