I cannot find the config file URGENT

[ekekakos]

Dear all,
I have an urgent issue and I need desperately your help.
I have a synology and I installed the Roundcubemail from the syno community which is the version 1.0.1. I user MySQL. I am trying to find the config file which is being used by Roundcubemail in order to add plugins but I cannot find. I have seen that the configuration of the user is in the USERS table of MySQL but I cannot find where is the file to add the plugins.
Can someone to help me?
Thanks

[SKaero]

It should be at <RC root>/config/config.inc.php

[ekekakos]

This config file is there but it does not work. It uses another one and I do not know which?