How to set up plex/qnap to run without internet access?

I am trying to set up a plex server installed on a qnap NAS to run without internet access. I’ve loaded the nas/plex server (accessing plex on my computer via internet access) with hundreds of movies. I want to be able to view those movies from the NAS/Plex server in my RV, on a smart tv. However, I’ve never been able to access plex when just plugged into the TV, it keeps looking for internet access because it is used to being accessed via the internet. When I plug in the RV’s smart TV via the HDMI cable, I launch the Plex app, it just lists ‘search’ options, it cannot see the local server with all of the movies. when I try to run the plex server, it says that “Plex is not reachable”. I’d really appreciate some help, I’m a Plex Pass member, but at 64 yrs old this is not my area of expertise. Thoughts and advice? thanks!