How to download watchOS 4.2 beta 4 to your Apple Watch

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.

Taken from – 

How to download watchOS 4.2 beta 4 to your Apple Watch