From FreeCAD Documentation
- download the workbench from github by clicking on the button “clone or download” on the github page (upper right corner) and choosing "Download ZIP"
- unpack the downloaded archive on your local hard disk
- within FreeCAD, locate the macro path by choosing “Edit > Preferences > General > Macro” and look for the ”Macro path”
- supposed your Windows-Login is “User-Name” the default macro path is “C:\User-Name\Appdata\Roaming\FreeCAD”
- within the macro-directory create (if not already present) a folder called “Mod”
- within the folder mod create a folder with the name of the workbench, for example “Assembly2”
- now move the unpacked files and sub-folders of the workbench to the just created workbench-folder
- after restart of FreeCAD you should now have an entry in the workbench-pulldown-menu