I attach a screen image of what you should be seeing.
If you are unable to see the small icon (shown in the image) then make sure that you have enabled Dreamweaver to show Invisible Elements.
Dreamweaver Menu > View > Visual aids > Invisible elements - Make sure it's ticked.
Then click the little icon (if you can now see it) and you should be able to see the CSSMenuWriter 'Edit Buttons' in the Properties Panel.