Assuming you have installed the SSD correctly, you should boot into [link|https://support.apple.com/guide/mac-help/use-macos-recovery-on-an-intel-based-mac-mchl338cf9a8/mac#:~:text=Restart%20your%20Mac.,other%20apps%20in%20macOS%20Recovery.|Recovery Mode|new_window=true] and reformat the disk for macOS in Disk Utility. If the drive doesn't show up in Disk Utility then you should check the compatibility of that drive to make sure it is usable with the MacBook Air. Once the drive is formatted, you can reinstall macOS in Recovery Mode. Good luck!