how to use Let's Encrypt with EHCP?

First of all a big PRISE. Having used Plesk and ISPconfig I always had troubles with email - but EHCP - surprise - Email worked out of the box - well. Some tweaking still needed, but otherwise excellent! (even Google accepts)

I'm using Ubuntu 18.4 with Webmin as a helper. Virtualmin was an option, but is really made for nerds and awfully time consuming...

Now to EHCP, the self-signed SSL for websites is working ok, but browsers doing silly warnings.
However, how to implement Let's Encrypt without trashing anything?

Can anyone give me some hints? I could invoke Let's Encrypt over the OS - not sure if this may have odd effects with EHCP.

Thanks in advance