In the Mixer there are only 2 tools available in the Tool Menus: Pointer and Hand. By default the pointer is the Left click tool, the Hand the Command click tool.
The instructions are to Hold Command (to get the default Hand tool) and Option (to copy the plugin rather than to move it), then click hold... drag the plug to another channel. Do not let go of either Command or Option until you have let go with the Mouse. Check that you have the Hand tool as the Command click tool.
Also when I click on the Amp Designer plug in on the Guitar strip the insert becomes blank - why is that?
Option Clicking on a Plugin or Send will bypass it.