How to reset administrator password On my iMac OS 9.5
Trying to reinstall operating system’s for my iMac
There isn't a single "administrator" on macOS. You can reset any user's password in various ways: Change or reset the password of a macOS user account - Apple Support
However, if you don't have another admin capable account, you can do this:
How to reset administrator password On my iMac OS 9.5