Using the command rscadm or scadm previously covered in this page you pass the argument userpassword <username>.
root@localhost:/ # /usr/platform/`uname -i`/rsc/rscadm usershow
username permissions password
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admin cuar Assigned
root@localhost:/ # /usr/platform/`uname -i`/rsc/rscadm userpassword admin
Password:
Re-enter Password:root@localhost:/ #