mac starts with a question mark

I'm not sure how you managed to erase the internal drive, if you had nothing else to boot from while doing it.

If the Mac still has Recovery installed, you may be able to use the Recovery system to reinstall a copy of macOS from over the Internet.

Intro to macOS Recovery - Apple Support

If you formatted the drive, it's showing you the question mark because there is no operating system to boot.

Did you use an external startup drive when you were reformatting the MacBook's internal drive? If so, maybe you could use that drive to start up the MacBook, so you can download a macOS installer or restore the internal drive from a backup.