You see at (4) and (5) its function is listed as "Mouse Button 4" and "Mouse Button 5". Those 2 are the default "Back" and "Forward" buttons.
Windows will recognize "Mouse Button 4" as Back and "Mouse Button 5" as Forward.
Click on "Go To Sideview" to access the 1-12 buttons, then set it to "Mouse Fuctions" then "Mouse Button 4" if you want Back.
EDIT: Lol I'm a bit late but I see you got it working now.
