I'm not sure I have the capability of blind walking you through directory copying and file editing on Windows if you've never done it before.  Usually my "go to" solution for this situation is to recommend hiring a kid in the neighborhood to come do it for you for a few bucks. Kids always know how to hack any computer.

Mostly you want to right click on the folder/directory, choose the 'copy' from the dropdown menu, hold down the ctrl key and tap the 'v' key. That should create a new directory renamed with a " - Copy" added into the name. You can edit your .json file in there for your remaining GPU's and then run the miner bat file from that new directory.