Security Certificate on Nextcloud FreeNas Plugin

I am using Nextcloud on a FreeNas jail plugin. I am trying to figure out how I can make it more secure by using a security certificate provided by a CA. I do NOT want to use letsencrypt or a reverse proxyserver. I have already purchased a wildcard certificate for my domain and prefer to use it since I do not have to continually validate and renew it. I am hoping to get help with creating a signing request and then importing the certificate back inside the jail. I currently have the 11.2 version of FreeNas installed and I am running Nextcloud 14. Any help I could get would be greatly appreciated.