If you ever need to make changes to a custom attribution model or extend the expiry date on a Test model you can do so by returning to the My Models screen.
From the left navigation bar, select [Altitude].
From the left navigation menu, select Attribution → Models.
Next to the model you need to update, select [Drop-down menu] → Edit Model.
Make the changes you need to make.
View the sections above for more information on each part of your custom model.