Sounds like you might have opted to sign-out all devices in the process of changing your password. This will also sign-out your server.
There’s no need to re-install anything… you’ll just need to re-claim your server (=signing the server into your account). You should be able to do that by connecting to the server, using the bundled web app installed on the QNAP:
make sure you’re on the same network as the QNAP!
open http://[QNAP IP address]:32400/web (no hostnames, DynDNS…)
open Settings and navigate to [Server Name] > General
click Sign In at the center of that setting page
As a side note… you might want to upgrade your PMS (unrelated to this situation).
PMS 1.32.1 was released in spring 2023 and won’t be compatible with the upcoming new players.