computer architecture – Hp Chromebook 15 original bios

Good morning all Someone here who can help me find the original bios of my HP Chromebook 15 when switching to full-rom bios I lost my backup of the previous bios and now I cannot revert to native Chromebook Rom, I’m having trouble with custom roms Like ubuntu, cloudready even galliumos .. I have to go back to my old ChromeOs which I can’t do because I lost the bios