To add the UMBus Root Bus Enumerator back try the following:
Go to Device Manager > Action > Add legacy hardware > Next > Install the hardware that I manually select from a list > Next > click on "System Devices" > Next > then under "Manufacturer" click on "Microsoft" then under "Model" click on "UMBus Root Bus Enumerator" > Next > Next
Restart the computer and the UMBus Root Bus Enumerator should reinstall.