You can try this:

1) Find your old iRedMail installation directory, for example, /root/iRedMail-0.8.6/
2) open the hidden file, .status, find all variables start with 'status_rcm_', for example:

export status_rcm_install="DONE"
export status_rcm_config_httpd="DONE"
export status_rcm_import_sql="DONE"
export status_rcm_config="DONE"
export status_rcm_plugin_managesieve="DONE"
export status_rcm_plugin_password="DONE"

3) Remove all lines contains 'status_rcm_'.
4) Re-execute iRedMail.sh script like installing iRedMail:

# bash iRedMail.sh

Good luck.

It won't install package, just config roundcube.

Oh, i forgot you're running FreeBSD, you should install roundcube manually first, then follow the steps mentioned in my previous post.