using plasma5, I disabled the right click mouse action in the rightclick>configure_desktop menu>mouse actions, now I would like it back but I cannot find it in system settings!! where the **** is it?? 
manythanks, ciao, pier
There should be a small gray settings box near the top left of the screen. Clicking that should give a menu. Select “Configure Desktop” from the menu.
:)maaaaanythanks, found