If you've downloaded FreeCAD for MacOS from FreeCADweb.org, you may find that upon trying to install the program, you'll get the message "FreeCAD" cannot be opened because the developer cannot be verified.
There is a way to override this. Click Cancel on this message and right click on the FreeCAD icon. In the resulting popup menu, select Open. You'll once again be presented with a warning, but this time, you'll have the option to open anyway.
Once FreeCAD is installed on your Mac, you can open Python files exported from BikeCAD Pro.