Deleted Macintosh HD, how to fix

While booted into Recovery Mode launch Disk Utility and erase the physical drive. You may need to click on "View" within Disk Utility and select "Show All Devices" before the physical drive appears in the left pane of Disk Utility. The physical drive should appear as something like "Apple SSD ....". Erase the physical drive as GUID partition and MacOS Extended (Journaled) if you are reinstalling macOS 10.12 Sierra, or as APFS (top option) if installng macOS 10.13+. After the physical drive is erased you can either select "Reinstall macOS" or "Restore from a Time Machine Backup".

This procedure will erase the drive and your data if you don't have a backup. If you don't have a backup, then it is extremely doubtful you could recover anything from an SSD even using a professional data recovery service.

Make sure it’s not hanging around somewhere, press the option key when booting and select the boot disk and press enter.

or else,

when booting press and hold command+r and enter recovery mode, and go to disk utility and check for other HD names “untitled” “uninitialised” etc. Hard disks don’t disappear physically by deleting their partition, so check for these names and you can reformat it as Macintosh HD and reinstall macOS.