watchOS 5.3 (build 16U5569a) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-07-16T17:14:15Z. The update package is 133.5 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: 564b894897788e90e2c931c8a9715cd91cb13881.zip.