In the bottom left-hand corner of a Report Preview is an ‘Edit Section’ button. Click ‘Edit Section’ to return a page identical to the Report Builder. If you want to make changes to multiple sections of your report, simply click ‘Edit Previous Section’ or ‘Edit Next Section’ to toggle through. You can add new sections at the bottom of the page.
From here you can act as if you are Building a Report for the first time; click ‘Preview Section’ when you have finished making your changes.