If you type /dopusdata/ConfigFiles into a file display, it will take you to where the ftp.oxc and ftpdef.oxc files are on your new drive.
You should be able to use that location to work out where they were on your old drive.
Before copying them, fully exit Opus using File > Exit Directory Opus, then copy the two files using Windows Explorer, then re-launch Opus and check that the FTP address book shows the right sites.