DKIM - Roundcube and swiftmailer

I need to update a roundcube instalation outside cpanel that is working fine, except for DKIM. I have no idea if we need to set up dkim inside roundcube or it gets the information form dns files, but, the situation is that dkim is working for emails sent from cpanel webmail and is not working from this other instalation. I also have a application with swiftmailer and I need to set dkim for it. right now It is sending email with a bad dkim, and I dont know how this is happening. For this, I have the application coder available to help all the time, if needed. I will accept bids for both services or just the first one.