In the photo you'll see what I searched and then I did what AI said. Except doing so was not correct and now my MacBookAir has no system on it and needs to attach to a drive to reinstall OS. Except this MacBookAir can only use BigSur. Since my Mac Mini is using Sequoia, I attempted to download BigSur which indeed download, but as soon as it finished my Mac warned me it couldn't be installed. Yes, I know, but I wanted the installer to then put on a drive. How do I download the installer from Apple?