1. Connect to your gamepanel with your given credentials here https://gamepanel.fragnet.net/Login
  2.  After you managed to login to your gamepanel go to Commandline Manager and create a custom commandline where you can edit the server name , world name and setting up a password (needs to be 5 characters or more), you can follow the gif for more details.  

         

       3. If your server was running the commandline will have restarted the server, or if your server was stopped just press start.
           At the end all should be working and now you only need to connect to your Valheim server.

        As a precaution since this is a new game and can create issues with the files we automatically make a backup every time the server is stopped to make sure the world will not be corrupted and the data to get lost.