After completing registration, or if you already have a team, click the "Create or Join Group" button and follow the path to join an existing private group. Then, when prompted, enter the following information...
Group ID#: 10789
Password: cov
I've got ones on about 4 websites. There is so many different sites with the game!
The sun
Official Premier league
Sky Sports
Mirror are the ones I'm signed up for but there's still another 3+ more!