cycle_valence cycles the valence on the currently selected bond.
cycle_valence [ h_fill ]
cycle_valence cycle_valence 0
If the h_fill flag is true, hydrogens will be added or removed to satisfy valence requirements.
This function is usually connected to the DELETE key or "CTRL-W". (Try CTRL-W first.)
There are two distinct ways to cycle a bond valence in PyMOL. First, if you start by clicking the Builder button you don't need to worry about Editing Mode, PyMOL will take care of that for you. After clicking Builder, click Cycle. In green text you should see, "Pick bonds to set as Cycle bond..." now just use the LEFT mouse button to click on a bond (not an atom). If you repeatedly click the bond, PyMOL will cycle the valence. The second method requires PyMOL to be in Editing Mode. To ensure you're in Editing Mode, please either click Mouse > 3 Button Editing. Now, using the mouse please CTRL-RIGHT-click on a bond (not an atom). The white cuff appears with a number (the angle of the substituents). Last, type CTRL-w to cycle the bond.