Using the created Nginx & Letsencrypt companion for SSL certs on a different server/IP address

[trueself-belief]

This may be out of scope for here but wanted to ask as i can't seem to get it.
I have this fully working which is great.

I am now looking to use the nginx + letsencrypt containers to help secure an SSL cert for a webserver on a different IP address.

Is this possible?

(I have set up a 'webserver.conf' file in /etc/nginx.conf.d/ - and this is proxying to the correct IP and working - without SSL)

I see how to do it if I wanted to create another docker container within the same server+network but can't figure out how to do it with an existing server on a different IP address!