Plese HELP - How To Install Comodo SSL For Postfix & Dovecot ?

Hello,
Beside PrivateKey file, I have 2 bundles of SSL files from Comodo and GogetSSL -

FYI I already installed the cert successfully on http level from Plesk UI. So its only for mail (SMTP, POP, IMAP) that I failed.

After I backup postfix_default.pem & ssl-cert-and-key.pem file I begin to...

Plese HELP - How To Install Comodo SSL For Postfix & Dovecot ?