If you have set a backup email address for the Gmail account in the event you lose your password then you should be able to reset and change your Gmail password by clicking on a reset password link which should then send you a verification code or a link.
When you get that reset password email you click on the link if they have a link in the email or enter a code into a box.
I haven't used Gmail in awhile so I don't remember whether they send a link or a code. But I think it's a link that you click on and once clicked it should take you to a page where you can enter a new password for your Gmail password.