Insert the Generic Product Key for your version at Settings > Update & Security > Activation > Change Product Key. This will prompt it to activate with a Digital License if there is one because a Proper Upgrade from the same lower version was previously activated on that PC.
It might also work if this is a Windows 10 PC that has an embedded Product Key in the BIOS which also has registered a Digital License in Activation Settings.
However normally embedded Product Keys are Home version. There's a chance your PC never had any Digital License, but had an older edition of Windows that was not Upgraded, which is why the seller or a shop used the illegal Volume License Key to activate it - technically piracy and a theft.