Blur text in iMovie 10.0.7
I found an apple discussion that seemingly answers your question:

Question


  I went to the help menu and it instructs me to click an icon that doesn't appear.  Any help would be greatly appreciated.


Answer


  Yes I had this problem as well, I found out that you have to Drag the clip from EVENTS into your PROJECT.
  
  But when you do so, make sure that you drag it just over the top, not actually into the clip. The icon should then appear.


I am sure that Video Overlay settings have the same reason to not show up as the Adjust option

Hope this helps