One week after releasing the first beta, Apple has now seeded the second build of iOS 10.2.1. This is a minor update, which, according to the release notes, brings some bug fixes and improvements. We were not given anything specific. There are no major UI changes that we have noticed.
Developers can find the latest beta from the Settings app. If you do not yet have the testing profile installed, you can go to the Apple Developer Center and find it there.