I purchased refurbished from Best Buy or Future Shop with Windows 7 Pro 64 I believe - may have been Home. At the end of May 2020 the hard drive failed. I also had a different computer with Win 10 Pro 64 and Office Pro 2016 installed on the hard drive. I preferred to keep the Dell functioning so I transferred the Win 10 hard drive to the Dell Optiplex 790. I now know Dell has not tested/approved this computer for Win 10. However it has been functioning since installed without incidence. Recently, I installed the most recent Win 10 Pro update and started gettting the message "your license is about to expire" go to settings. In settings it says "Windows is activated using your organizations activator service". I tried several options (connected and not connected to the internet) to get rid of that message using "slmgr" and error message "0xc004f074" is as far as I could go. I was able to restore Win 10 prior to the update and no more problem with that error message. However, I am not sure and would like to know if the problem is Dell related or Best Buy/Future Shop related since the Optiplex 790 came to me with Win 7 Pro installed. 

Does anyone know if there is some setting in the bios to correct this so that I could use my Win 10 serial number?

In the process of going through all this I have updated the bios from A07 to A10 and then to the current version.