Hello, My watch,Forerunner 945 LTE, is stuck on update, gear wheel with down arrow. Can you help me unlock the watch? Thank you for your help.

https://support.garmin.com/en-US/?faq=waEtGnqrqpAjZ9Eg4iF7HA

Had this happen once with my Instinct 2 Solar.  Hold the light button until the watch shuts off.  Turn back on and install should continue.

I'm having the exact same problem with a watch I've only had for a week.

This is the answer I received from the service desk, this did not help me because the watch immediately jumps back to the same screen, but maybe it will help you:

We recommend that you perform a Hard Reset of your watch:

1. Press the "Light" button - your Forerunner will turn off.
2. Press and hold the "Enter" button (top right) and the "Down" button "bottom right"
3. Briefly press the "Light" button (while holding down the "Enter" and "Down" buttons) - Forerunner will turn back on.
4. Release "Enter" after the first beep (press and hold the "Down" button)

NB! This will erase all data you entered and your activity history.
Select delete data and restore settings

This does not work. IT still gets stuck in the Update. Frustration. Any other ideas? 

I contacted Garmin and they asked me to send the watch back, so I did and I'm now waiting for their reply.