Copy your key from the text document.
Load up you target firmware that you are flashing to the drive.
Click on Manual spoof
In the top box it will have most probably "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
Paste key over this.
Press Tab key and the OK box will now be available to select.
Press okay, and your key is now ready to flash over.
You can then save that to a file with the "save to file" button.
Save the firmware and keep safe