how to reset password for ubuntu GCP instance

C++
vfa_gianglt@instance-1:~$ sudo -i
root@instance-1:~# sudo bash
root@instance-1:~# sudo passwd root
Enter new UNIX password: 
Retype new UNIX password: 
passwd: password updated successfully
root@instance-1:~# cd /root
root@instance-1:~#
Source

Also in C++: