@sharno18 . Your Plex server needs a reserved ip address in your router, outside the dhcp range of the router.
Set up port forwarding. Forward the Plex port (32400?) to the Plex port on the Plex server.
Set up Dynamic DNS so you can find your home network without worrying about public ip address changing.
There other threads in Community on Plex from other users. Put plex in the search bar.
Can you describe your setup a bit?
Does your remote device have a Plex client that directly connects to the Plex server at home?
Alternatively, does your remote device and your server both connect to Plex web site and exchange info?
Did you set up DDNS so you can access your server using a name rather than public ip address?
Does the Plex client accept a host name instead of an ip address?
What model router do you have?
Do you have all the ports and TCP/UDP protocols forwarded?
Any messages on the remote device when you try to connect?
Something more complex to try. Connect your remote device to your home network.
In command window, do netstat -an command. This shows all the network connections on your device.
Get the Plex software going and connect to your server. Do netstat -an again and compare the connections. You're looking for connections between your device (Local address) and the Plex server (Foreign address). Note the Foreign port numbers; you need rules for them.
If your remote device can't do netstat, do it on the Plex server and swap Local for Foreign.
@sharno18 . Do you have the router from your previous provider or can you borrow a suitable one? Won't matter what it's like. You're wanting to test the mechanism of port forwarding and the Plex setup.
If you're using the TPG router, you could try enabling UPnP.