Once you have finished setting the mapping options you will be taken to the main Chart Designer interface. Once you are in the Chart Designer you can return to the Data Mapping window by selecting Data → Modify Data Mapping, or by clicking the Change data mapping icon. This will return you to the data mapping screen, allowing you to adjust the mapping for the chart.

You can also change a data source directly from the Chart Designer by selecting Data → Modify Data Source, or by clicking the Modify data source icon on the toolbar. This will open the Data Source Manager.