If you have chosen the Direct Selection option, once you have completed the file selection the Report Definition page is shown:
Use Report Definition
Check the box Use Report Definition in order to use any existing report definition file to define the lines on your report/graph. Alternatively, un-check this box in order to create reports with lines defined by the basic database hierarchy.
This allows you to conveniently view or edit the currently-selected report definition. Upon returning to the wizard, the updated file will be used.