When you add a Choice to an action card, the Default option is set to do nothing. This means that this action will not be taken on anyone who does not meet the criteria for previous Choices.

You can set the Default Choice to be something by hovering over the Default Choice and clicking the edit icon:

The next step is to fill in the required values for the action that you are defining the default choice for. Since our example uses Change Account Datawe are going to choose an Account Field, and a New Field Value and click Save.

Thats it! Now anyone who does not meet the criteria of any of the Choices you have defined criteria for will be added to the Account Field that you selected as the Default Choice.