Move the DLL and GHA files to Grasshopper's Components folder, which you can get to from File → Special Folders → Components folder, or you can navigate to it manually: C:\Program Files\Rhinoceros 4.0\Plug-ins\Grasshopper\Components\
Right-click the DLL and the GHA files and select Unblock.
The exporter should now be available under the S tab.
How to use
You will need these components in your Grasshopper Canvas:
The Sketchfab Exporter, found in its own component tab