i forgot my computer password

Hello,

One option is to simply reset it with your Apple ID... To do that enter the wrong password three times and enter your credentials. If that is not enabled. The other option is to use another admin account you have access to then reset the password of the account you are looking for.

There is a last option... Go intro recovery mode (CMD+R while the Mac is starting up...). Open terminal and type:

resetpassword

PS: Do the right thing, if this is not your Mac return it to the owner. Also, I don't know if the last one still works...

More information.

User Password Reset.   

User Password Reset (2).         

User Password Reset – Apple ID.