Along with the new beta versions iOS, macOS and tvOS today Apple also released the second beta of watchOS 5.1.3 for developers.
It's only been a week since the first beta was released. The new version can be installed via the app Apple Watch to iPhone with a developer profile.
Given the 5.1.x version number, it can be assumed that this will be a minor update with bug fixes and other improvements. No new features are expected.
Nevertheless, we will definitely inform you if we find something new in the new version.