How to restore 1st gen. Apple TV

Hi guys, I’ve a .dmg file of the 1st gen Apple TV’s 1.0 OS, how can I restore my 1st gen Apple TV with that .dmg?
I tried restoring the DMG onto an USB stick with Disk Utility, starting up the Apple TV with the USB plugged in the USB port and then “Menu + Volume down” on the Apple Remote but it just redirects me to the Apple TV Recovery, and if proceed for restoring it just restore again the 3.0.2 OS, which is not what I want to do.
I then tried to convert that .DMG in an .IMG image and restoring it on an USB stick with ApplePi-Baker, and try again starting the Apple TV from the USB stick, it just boot again the Apple TV Recovery.
How do I need to do it? Thanks