watchOS 5.3 (build 16U569) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2019-07-22T19:16:53Z. The update package is 173.66 MB. This is a delta (partial) update that requires 5.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: f22d04228aca801084d572e9b3f46cafc0269487.zip.