How to download watchOS 4.1 beta 4 to your Apple WatchInstalling the watchOS 4 beta is more complex than an iOS or macOS beta, but it's also for developers only.
There's yet to be a public beta for watchOS the way there has been for iOS and macOS, and that's okay — the process of 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 11 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.
How to download the watchOS 4 beta certificate
How to install watchOS 4 on your Apple Watch
How to downgrade to watchOS 4
How to install the watchOS 4 beta certificate
Note: Make sure you're running the developer beta for iOS 11 on your iPhone before trying to install watchOS 4.
Log into developer.apple.com on the iPhone paired with your Apple Watch.
Go to the watchOS 4 download page.
Tap on Download watchOS 4 beta Configuration Pro...
Source:
How to download watchOS 4.1 beta 4 to your Apple Watch
