https://wccftech.com/download-watchos-8-rc-update-for-apple-watch-now-available/

Apple has seeded the watchOS 8 RC update for all compatible Apple Watch devices. Developers and public testers can download it now.

watchOS 8 RC is now available for download if you are a registered developer with Apple or just a public beta testers. Just like any other update for Apple Watch, this one is available over the air as well. Follow the steps below and you will be running the RC build in no time: