Quit FCPX.
Move the sc_magnifier (and all its contents) to the desktop (temporarily).
Open sc_magnifer folder and Move the Magnifier folder into the Instructional Aids folder.
You can delete the sc_magnifier folder if you like (other than the installer information in the Magnifier.png image, there's no further use for it.)
Restart FCPX.
Find the effect in FCPX in the Effects browser:
Drag the effect from the browser onto a clip into the storyline. Change parameters in the Video Inspector on the right side of the canvas. The Magnifier effect should be at the top of the list.