How to reconnect to Plex server NVIDIA Shield

Server Version#: Latest (d/l and installed yesterday)
Player Version#: Latest (d/l and installed yesterday)
<If providing server logs please do NOT turn on verbose logging, only debug logging should be enabled>

I had a Plex server set up on an NVIDIA Shield, which I disconnected when I bought a new computer and an Apple TV device. Now, I’ve added a new Denon AVR and want to reconnect my Shield and the external HDD that contains all my content. However, despite reconnecting it all and reinstalling Plex, I have no idea how to connect back to that specific server. I have a load of home movies and my entire music catalog on it and would hate to lose it all. I would greatly appreciated any help that can be offered as I’m not very knowledgeable about this. Then, any tips on how to avoid this in future.