Hi UnrealCry,
If you have linked your GitHub and Unreal Engine accounts, and joined the Epic Games organization on GitHub, you should be able to go back to the VXGI branch that Nvidia has and download the Engine from there. If you download the Engine from this branch, it will include VXGI.
You would then just need to run Setup.bat, then GenerateProjectFiles.bat, then build the Engine in Visual Studio. You can find some more information about getting started with GitHub here.