HI, this is Mag, last week I had my MacBook repaired in the Apple store and they installed the Big Sur for me. After that, I entered many times of my password of logging in, it just couldn't let me log in anyway. I couldn't change my password too

I don't know why after the apple store helped my installed the Big Sur, then I couldn't log in with my original password anymore. I've search many options and solutions online and tried all of them, it just couldn't work at all. It also didn't show that there's an option of changing my password with my Apple ID, so I don't know what to do now. I'm stuck and confused why I can't login anymore. Please assist me asap! I appreciate it.

Mag