How do you get any certificate to work in Apache? (Usually you need to point to the fullchain.pem certificate file and the corresponding key file in the VirtualHost configuration. Don't forget to reload after renewals.)
https://httpd.apache.org/docs/2.4/mod/mod_ssl.html#sslcertificatefile
They both work the same way.
http://www.postfix.org/TLS_README.html
https://doc.dovecot.org/2.3/configuration_manual/dovecot_ssl_configuration/
If you are asking how to use certificates obtained on one host on a separate host, the question may now become: "How do you copy other files between these hosts?"
I like rsync over ssh using keys myself. You can even restrict the commands that can be run by the ssh key you create for this role. Whatever routine you devise will need to be called by a deploy-hook and should trigger a reload of the services using the certificate.