New Apple Watch stuck on installation

I was recently given an Apple Watch 3 from a friend who got a newer model. I erased all the data on the watch so that it could be paired with my iPhone, and then I downloaded the Watch app and began the setup process. The app told me I needed to update the watch to the most recent watchOS, so I agreed to all the conditions and began the installation process.

That was about 16 hours ago, and the app still shows that the update is “Installing”. The watch says “continue setup on iPhone.” My phone has been within range of the watch and connected to wifi this whole time, and the watch has been on the charger (obviously not connected to wifi because it’s new). Any ideas what I can do?