For an existing refinement rule, you can add attributes, change the selected attribute for a data set, and remove attributes.
To change the refinement rule configuration:
If there are no additional attributes to add to the rule, then the add option is not available.
When you click the + button, the Edit Refinement Rule dialog displays. At the top of the dialog are the currently selected data sets and attributes.
If there is only one available data set, then it is selected automatically.
You can also click the attribute, then click Add to Rule.