28,657 questions
Go to any reputable site such as NewEgg or CDW and find a digital Windows 10 Pro license. Ensure it is the 64-bit download version. Buy the license to get the product key.
Go into Windows Activation and use the Change product key
to enter the new key. You might need to reboot but you should be good to go after that. Note that if you're using an MS account then the product key is associated with your MS account and you should no longer need it when reinstalling Windows.