performing reset root password on Google Cloud Platform ?

hi,

i want to know how to performing reset root password on Google Cloud Platform, i've been following this document reset root password, but when i trying to access single user mode in serial console there's no counts at booting mode

and when i try to attach boot disk image to another instance, i can't find

passwd

or

/sbin/passwd

command

can you give me guidance or link document regarding this problem ?