This command is only enabled if the currently selected file or folder in the File Browser has duplicates.
For files it simply steps to the previous entry in the Duplicate Files Browser.
For folders, the previous folder in the list of duplicates of the selected folder is selected. Note that the only ways to view the duplicates of a folder are either to step through them with this command or the next duplicate command, or to use the duplicate folders report from the report panel.
Keys: Shift+F10