This is because you selected the incorrect SHARED campaign box.

Instead of entering the share code on SHARED CAMPAIGN, you need to enter it under 

COPY SHARED CAMPAIGN  (the box on the bottom.... not the top...)

Once you do that you'll be able to edit the fields.

David shows you CLEARLY how to do this in the video, so make sure you watch it at least 2-3 times before attempting to do this.