How to recover password on Mac OS?

Question

macOS

The wife calls and says that when you turn it on, you need to enter a password. No one set a password, BUT: before that, when they played chess on the computer (a standard game on Mac OS) and decided to save either their progress or the result, the system asked them to enter a password. They created it, then turned off the computer, and now they don't remember the password and can't log in.
Colleagues, has anyone experienced something similar? What can be done? I don't want to reinstall the system.

Answer 1

It’s hard to say remotely what happened to them, in general, they say that they rebooted by pressing a button on the device itself, as a result, the computer turned on normally without asking for a password.

Answer 2

Try entering an empty password. If not, then most likely you will have to demolish the system and reinstall))

Answer 3

Resetting your password with your Apple ID
If you have linked your user account to your Apple ID, you can use your Apple ID to reset your login password.
Choose Apple menu > Restart, or press the power button on your computer, then click Restart.
Click your account, click the question mark next to the password field, then click the arrow next to "reset it with Apple ID."
Enter your Apple ID and password, then click Next.
Follow the instructions to reset your login password.
Source: https://support.apple.com/kb/PH25720?viewlocale=en...