1. By holding CTRL + ALT down and clicking on Any Zbrush Interface Items, you will enter into Hotkey Assignment mode.
2. As the instructions mention it, Press any Key combination to assign custom hotkey -or Press ESC or mouse button to cancel, -or- Press DELETE key to remove previous custom assignment .
3. Type “K” on your keyboard, or CTRL+K or any other key. Make sure to not replace a vital hotkey assignment