How to download watchOS 3.1 beta 3 to your Apple WatchInstalling the watchOS 3.1 beta is more complex than an iOS or macOS beta, but it's also for developers only.
Update October 12, 2016: Apple has just released watchOS 3.1 beta 3 for developers. If you already have a previous watchOS 3 beta installed, proceed to the Watch app on your iPhone running iOS 10 and download away. If you're looking to jump into watchOS developer releases with beta 3, keep reading and we'll walk you through the set up!
There's yet to be a public beta for watchOS the way there has been for iOS and OS X, and that's okay — the process for installing the software is more complicated, and really meant for developers only. You need to install a certificate on your Apple Watch, then download the software to your iPhone running iOS 10 beta, transfer it across, and get it up and running. It's not hard, but it does take patience and you may have to troubleshoot.
Apple occasionally offers updates to iOS 10, watchOS 3, tvOS 10, and macOS Sierra as closed develo...
Source:
How to download watchOS 3.1 beta 3 to your Apple Watch