After you have created your join, you can modify it through the Recipe recipe panel. When you click edit the recipe step in the panel, the join step is loaded into the Join page, where you may edit your join's datasets, keys, included columns, and join type before adding it back to the recipe.
NOTE: If you modify the selected dataset to join, the joined dataset, the join keys, or the fields to include in the output, subsequent steps in your transform recipe can be broken by the change. After you modify the join, you should select the last step in your recipe to validate all steps in the recipe.
For more information on creating or modifying joins, see Join Page.
Tip: From Above the Recipe panel, you can click the Undo button to revert the last edit to your join step.