watchOS 5.3.1 (build 16U6600) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm), released on 2019-08-26T17:16:37Z. The update package is 120.87 MB. This is a delta (partial) update that requires 5.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 3f93c5852d2926f9154f8dedb760dcd9b443636e.zip.