That Addon was last seen in 2.79; since 2.80, there are no longer Layers in Blender (they have been replaced by the more powerfull Collections), so there is also no longer a use for a Layer Management.
Where would I locate the accent grove key in Blender? I am looking at a tutorial and Mr. Trimmel is using Blender 2.9 and many of the buttons have changed.
Martin already answered you in another thread, but just in case someone else sees the question or gets here by google, the accent key is the one below the esc key, with the squiggly line ~