If you've got yourself in a pickle with a report and you’re not sure what you’re looking at anymore, you can reset your report back to its original state!
First close the report by clicking the Close Report button (first button on the left of the top menu).
This will take you back to the main Reports Screen.
Single left-click on the report you want to reset and then click the Delete/Reset Report button (Third button from the left on the top menu).
A message box will ask if you want to reset this Report to its original state. Click Yes.
Your Report will now be reset to the default state. Now you can go back into the Report and start modifying it again!