Can't access one of two user account on my MacBook Air.

I couldn't log in to my business user account on a new Mac. I used the personal user account hoping to change the business login password. A pop up message says this will not change my login password for the business account and I should use the Utilities-keychain access to do so. I went to Utilities-keychain access and saw two login passwords - one is listed public and the other is listed private.

I don't know which one belongs to which user account. I opened up a second Mac Air and see it also has two login passwords even though this Mac does not have two users.

I am now confused about the public login key. And I still don't know how to change the login business user account on the first Mac. Just to note, I already tried to restart Mac #1 to reset my business user login password but it said the apple account I used (my business account) does not have permission to load the volume (?).

I tried Genius Bar but couldn't find the topic that would get me an appointment. Thanks in advance for all your help.