Players can unregister from a tournament before deck list submission closes through the Player Dashboard. Navigate to the Player Dashboard and click on the tournament name to go to the tournament dashboard. Click Your confirmation to view your registration confirmation. If deck list submission hasn't closed yet, thebutton is shown; click that to unregister from the tournament.
If deck list submission has closed, you will need to reach out to the tournament organizer and request that they delete your registration. Once that’s done, verify the registration is no longer in your Player Dashboard.