Apps trying to connect to old server

I have migrated to a new Plex server and transferred settings (as much as I could) and I’m running into an issue with the clients - apps on mobile and Roku. They keep wanting to connect to the old server and display most of the libraries twice (old and new server). How do I stop the old server from coming up in the lists?

Is your old server still running?

It is still physically running, but Plex is no longer running.