I can’t see any computers to sync to on my iPhone.
After updating to iPhone Update Service using Principalm Connect you should be able to open Principalm+ on the iPhone and on the Sync/Download screen see your computer listed.
If there are no computers listed the reason is most likely because your local computer (where you are running Principalm Connect) is not on the same subnet as your local WiFi.
This article explains how to connect to a different subnet via your iPhone: iPhone: Connect via different subnet