It’s the screws behind the pen holder. Not the black screws on the actual holder, it’s the silver screws that holds the holder in place. It’s actually different looking than the user guide. Hope the pic below works.

http://s1156.photobucket.com/user/Wavertree/media/5C9CE226-D302-417D-B9F6-28E9C6012664.jpg.html