Since the computer will boot into Internet Recovery Mode But this does Require an Active and Functioning Internet Connection
Predicated on the above as working >>
Understand the Below will WIPE ALL DATA and there is No Recovery - Period.
1 - It will present options >> Disk Utilities >> View >> View ALL attached Drives.
2 - Choose the Upper Most Drive ( not the volumes indented and list below ).
3 - The drive normally is called Apple Media or Apple SSD - that is the drive to Erase and format as APFS with the GUID Partition Map. This applies to macOS 10.14 Mojave and above.
4 - Once that is done >> backup out of Disk Utilities and choose install macOS.
5 - Follow the prompts and it may automatically reboot several time.
6 - Upon a final reboot - Setup Assist will present with the newer version of macOS.