Change password for Administration

Change or reset the password of a macOS user account...

https://support.apple.com/en-us/HT202860 

My Mac mini is trying to install Catalina. I'm asked for an administrator's password, which I do not have. I set up the computer myself. How do I find the administrator's credentials?

Also, my cursor disappears from my screen. Is this related or a separate problem?

Any luck?

I forgot my administrator password, and i need it to update to the latest operating system