How to change password postmaster

[jaja triharja]

Hi ! I am new member in this milist, I'm form Indonesia.
So, sorry about my English...

I just used vpopmail and qmailadmin, some one has created virtual domain
with vadddomain before. Now, I loss postmaster password. I try using
vpasswd to change that password but not success, with the error Unknown
virtual user.

Thank you,

ja3