it was previously connected to a wifi network and its password changes.

it disconnects and won't automatically reconnect (rare, might happen after an outage).

You need to swap to a new network.

Remove the cover on the back. Locate the dongle, and remove it, while remembering the USB port. Good way to remember which one is as "the one closest to SW button".

Turn the printer off (using power button)

Grab a paperclip or pen.

While off (but still plugged into power supply), press and hold the SW button using the paperclip or pen; afterward, and without releasing SW button, press power button once to turn it back on.

A few seconds later, a receipt/label will print, indicating reset in progress. Release the SW button.

A second one will print 30 seconds later, signaling reset being completed.

Reconnect Dongle(see first bulletpoint to remember USB port)

Restart printer by pressing power button off and on again.

Wait for receipt reading "Simple AP" (and QR code, if label printer) to print, and WiFi light to turn steady.

Go through Regular internet Setup Guide to reconnect to a network!