How can I reset password for macOS Catalina on my iMac?

I partitioned my hd to add catalina to a 2013 imac 27. I now have both Mojove and Catalina loaded. But...I am unable to get my password to work on the Catalina side. I tried reloading Catalina, but there was no prompt to register a pw.

How can i reset the password for the Catalina side?

Thanks in advance

Pawdaddy

[Re-Titled by Moderator]