Reddcoin Wallet Recovery HELP!

Hi, My wallet was installed on an external hard drive; when I backed it up it saved the backup file to my computer in C drive so I moved that to the external drive as well for security intending to also backup to a usb stick later. This was just a few weeks ago. I had deposited some coins at that time as well. A few days ago when I tried to open the wallet it acted like I had never initiated or synced it and so it synced the whole blockchain again from the beginning and no coins show up. I had deleted the files stored on c drive because I had copied them to the external hard drive.
I have the backup dat. file but I don’t know how to use it to recover the coins. I read here that you can use it to “overwrite” the newer files but can someone explain how I do that? Thanks!

Check the backup and restore parts over here: