I can't change keyboard shortcuts
I am starting out with Premiere Pro CC and I need to change the shortcuts. I have read the support page on this:
Preset and customizable keyboard shortcuts in Premiere Pro CC
However, I can't figure out how to actually change a keyboard shortcut. What I want to do is change the zoom in to the + sign. So I get up the keyboard shortcuts window and finds that + is not assign, but how do I actually change it? Clicking on the command section is the below table has no effect. What to do?



