Restoring older chromeos

Recently I failed to update pacman with
$ pacman -Syu
but it failed and partial update messed my arch system at all. So I decided reinstall arch on my chromebook.
I found when I run install.sh script that parted is not working. And this suggest that I need older version of chromeos. So I download older os on my mac and burned it on the usb and resotred my chromebook