Cannot pair or use my Apple Watch Series 3

I have an Apple Watch Series 3 on which I tried to install and update, and the update did not install. Now I can't use the watch and I am unable to find the serial number on either my phone or the watch so I cannot contact support. I let the install complete for hours, and it seemed to complete. However, I was then unable to pair. I tried the steps several times and also rebooted both the watch and the phone. The phone and watch keep telling me that they need to be paired, and then I am required to try installing the update again.

What do I do to resolve this? How can I contact support without being able to access the serial number on either my phone or watch? My watch does not include the serial number on the back.