Can not let virtual mail user to change their own password via webmail

Hello everyone.!!!
I have prepared a mail server recently. I installed postfix, dovecot & roundcube on ubuntu 20.04. I installed roundcube via apt-get install and it installed roundcube 1.4.3. In dovecote configuration (/etc/dovecot/conf.f/10-auth.conf) I have below configuration>>

disable_plaintext_auth = yes
auth_mechanisms = plain login !include
auth-passwdfile.conf.ext

In /etc/dovecot/conf.d/auth-passwdfile.conf.ext file I have below configuration:

passdb {
driver = passwd-file args = scheme=PLAIN username_format=%u
/etc/dovecot/dovecot-users}

userdb {
driver = static args = uid=vmail gid=vmail
home=/var/mail/vhosts/%d/%n }

And I have listed my virtual users at dovecot-users file in below format:

user@domain:password

virtual Users login/logout, sending/receiving mails are working fine through roundcube.

But I can not figure out which password driver to use and how so that my users can change their own password. It will be appreciated if you look into my issue and help me.

Thanks in advance.