I forgot my admin password how do I log in?

Because the details on how to perform this action (if not later system build macOS)

are not applicable as described in that later Support article ~ you may need to see:

• Mac OS X (10.6 & Before) -- Resetting a Forgotten Account Password:

https://kb.wisc.edu/helpdesk/page.php?id=3853

• Five Ways to Reset a Lost Administrator Password - TidBits:

https://tidbits.com/article/14437

Also covered, is some reference to Resetting the Keychain Password.

Your much older PowerMac likely isn't going to see help from iCloud.

{..Hopefully any who follow will read details & product vintage addressed here..}

Change or reset the password of a macOS user account - Apple Support