Share Internet from Windows 10 to Mac OS X via Bluetooth

I have managed to share Inteet from my MacBook Air to my Windows 10 netbook successfully.

But sometimes I'm using the Windows computer as the primary one for various reasons and want to share in the opposite direction.

I can't seem to find decent instructions I can follow for this particular arrangement. The GUIs and terminology involved seem to be quite different between the Windows and Mac universes.