If you run a report of the following types to a browser, then a button labeled Edit Saved Report will appear on the menubar of the report output:
Within a workspace, when you click this button, a new panel opens with the report editor. Note that you are opening the saved report. Be aware that if you have another panel open with the same report being edited and have changes that are unsaved, these changes will not be reflected in the panel you just opened.
Outside of a workspace, the Edit Saved Report button will open a new browser tab with the report editor.
You cannot edit a report from the output unless the report has been saved, but in most circumstances you will still have the report editor open at that point.