Brand new Apple Watch won’t update or pair

This is a never before used series 4 Apple Watch. I am trying to pair it to my phone (13 running iOS 15.5). This is my very first time using it, so I am setting it up. Although it does pair at first, it won’t complete the process because it needs to update the watch to iOS 8 first.

The Apple Watch app’s progress bar has said “three hours remaining” all day now. Sometimes it goes down to two, or even one, but then it jumps up to four or five hours remaining. It’s stuck and won’t update, so I cannot set up the watch. My phone is on WiFi, directly next to my watch, which is charging. AFAIK I have met the requirements to update.

Things I have tried that didn’t fix the problem:

-turning my phone off and on again

-same with watch

-resetting watch to factory settings (it already is on factory settings, it’s never been set up)

Things I cannot try:

-I’ve seen this suggested online: going into the Apple Watch app and deleting the update, then downloading it again. But my phone’s app has no settings because I haven’t paired the watch. The only button I can press right now in that app is the one that pairs the watch.

Any thoughts? This is driving me nuts.