watchOS 5.3 (build 16U5569a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2019-07-16T17:14:38Z. The update package is 115.65 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: 84cdf79babef8602fe92d9a6c9dc23b653b003f2.zip.