How to install Webmin on existing Apache + Let's Encrypt SSL configuration?

Using this guide for reference: https://www.digitalocean.com/community/tutorials/how-to-install-webmin-on-ubuntu-18-04

Currently have Apache + Let’s Encrypt SSL configured and working fine, plus a reverse proxy for Discourse in a Docker container. I was able to follow all points of the Webmin installation until I was tasked with obtaining an SSL certificate, which won’t work as I already have one. I tried just skipping that part but Webmin doesn’t appear at mydomain.com:10000 or mydropletip:10000, with or without https in the URL.

My vhost file looks a little different from the guide because of the aforementioned server configuration.

<VirtualHost *:80>
	ServerAdmin mygmail
	ServerName mysite.com
	ProxyPass / http://localhost:10000/
	ProxyPassReverse / http://localhost:10000/
	ServerAlias www.mysite.com
	DocumentRoot /var/www/mysite.com
	ErrorLog ${APACHE_LOG_DIR}/error.log
	CustomLog ${APACHE_LOG_DIR}/access.log combined
RewriteEngine on
RewriteCond %{SERVER_NAME} =mysite.com [OR]
RewriteCond %{SERVER_NAME} =www.mysite.com
RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>

Is there any way I can manually configure what I need for Webmin to work?

Thanks!