What to do if you accidentally delete your disk whiles factory resetting
What to do when you accidentally delete your startup disk
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You can try and hit cmd+r when booting to boot from recovery and install macOS again.
If this is not working, you can when you have access to another Mac, make a bootable macOS installer and boot from that (hold option at startup) and install macOS again that way
How to create a bootable installer for macOS - Apple Support