Resetting the password for a user if we don't know changed password

How can we reset the password or create new user on RPi and switch to it? I'm trying to help someone with their RPi issue, they got a ready project from someone else. They have custom user prototype and the password to this user is unknown. I'm trying to set up VNC connection on LAN network from their laptop to their RPi but we don't have the password for the user. Is there an easier way to solve this? Like creating a new user from the existing user and logging in using the new user? Or are we going to have to reinstall the whole system if they won't be able to contact the previous owner and get the password?

A minute later: they got the password from the previous owner. But I'm still interested: is there a way out of this without reinstalling the system?

https://www.debian.org/doc/manuals/debian-handbook/sect.creating-accounts.en.html https://www.debian.org/doc/manuals/debian-handbook/sect.user-group-databases.en.html And your friend and helper for every command in the terminal

--help

and

man

e.g.

apt --help

or

man apt

do u have root access?

if so u can both create another uzer for it and reset the password

sudo commands work, yes

then do sudo su

and after that

do passwd prototype

What will sudo su do? Substitute user google says?

But it says it'll ask me for a password?

u can just do su -

it'll put u into a root environment

after ure in root environment u can do passwd prototype and change the pass