When you say 'this' please be clear. The RBZ for the SketchUcation toolset which also control the licensing and ExtensionStore dialog etc is easily installed using the native Extension Manager > Install... button. Restart SketchUp afterwards to sync everything. It appears in its own submenu under Extensions and there is also a Toolbar.
LibFredo6 is not needed for the toolset, but it is vital to all of Fredo's extensions.
If you have not installed SketchUp itself 'properly' then you do not need to Uninstall and Reinstall it, instead close SketchUp, then find the SketchUp Installer's exe file in your Downloads folder [or download a fresh copy]. Select the exe file's icon, right-click > context-menu > Run as administrator - a dialog should open, accept the 'Repair' option, this will reset all of the permissions properly so extensions can install and save preferences etc. In a few rare case with some of Fredo's stuff a further manual deletion of a badly permission-ed subfolder etc is occasionally necessary, but let's cross that bridge as we come to it !