Returning to the default Linux system

Hello everyone, I have a LG super multi NAS which has a standard warranty with it. It comes with a Hitachi deckstar pair with 1TB of hard drive. I tried to install Microsoft Windows 7 on it, so I removed the previous drivers and formatted the hard drive.
It installed without any issue, but I somehow managed to format the drives using the Linux based file system. I managed to install windows 7 on it, but it’s doesn’t run correctly. I want to install the default firmware back on it. That is a Linux operating system, but when I tried this I get an error:

