It appears that I first have to do an upgrade of my Win7 OEM install to Win10 - which will turn my Win7 key into a working Win10 license. It looks like the only way to get it. So I'll have to do an upgrade and then wipe the drive and do a clean install.
Would definitely like to get a new drive to put it on as well, rather than this old drive I'm using.
Instead of wiping out a perfectly good Win7 partition install, can't you just make a couple primary partitions on the hard drive (or SSD) with Win7 in one partition and install Win10 to the second partition? There are free hard disk partition utilities and boot managers that can select which partition to boot from on system boot too.
Then you can switch between them until sure you want to stick with Win10 or until you gradually get all apps installed for Win10.
I did this back when I first wanted to try Win7 while using WinXP years ago, actually had 3 primary boot partitions:
1) DOS/GRUB utilities
I also have a fourth partition just for data.
I could boot into WinXP to play old games, etc while using Win7 for normal stuff.
Now I don't have the WinXP partition anymore since I upgraded to a SSD drive, so I could use the 3rd partition for making a Win10 partition at some point but still have Win7 available since I've heard Win10 has some compatibility issues with some old apps/games and drivers for older devices?