You can edit a team as having forfeited by ticking the "forfeit" box under the team concerned when you enter the score.
To do this, you have to put the date that was planned for the match, and then you can enter the scores / stats. And tick the team as "forfeit".
You will still have to input the score according to the rules of your championship.
For example, if in your championship the forfeited team "loses 3-0", it will be necessary to input the 3-0 to have an up to date classification.
The number of points for a forfeit can be set in Leagues > Settings > Standings