How do I reset my MacBook password if I forgot it and what I thought it was is not working

How do I reset my MacBook Air password? I entered what I thought it was (my son set it up and reset set it recently). I have tried every variation and it is not what I had written down. It doesn't give me an option to get a hint and it was not set up for any additional users. I do not want to restart it since I do not know what the password is.

Is there a way to reset the password (this is a 2nd hand MacBook - I am not the original owner, purchased used/factory reset). I have researched online and the Apple supports I found all state the same thing (system preference, User & Groups, enter your old password then new. I cannot enter the old one - I don't know it!)