In your game panel file manager navigate to data folder
Open data/server-settings.json
Within this file find
"visibility":
{
"public": true,
"lan": true
},
"_comment_credentials": "Your factorio.com login credentials. Required for games with visibility public",
"username": "",
"password": "",
Enter the username and password you use to log into factorio.com
Restart your server
It should now appear in the server list.