How to resolve password lock out issue on a new Mac mini without internet access?

I got a new Mac Mini, but wasn't able to use it more than a couple of times at my last location, and since then I've moved. I forgot my password. I was able to change the password by using my Apple account, but not with the Mac Mini, which was not connected to the internet. Now it locks me out, I guess because it cannot get the change of password because it cannot sign in to the access point. Any suggestions? Thank you!

[Re-Titled by Moderator]

Original Title: Password Lock Out Issue