watchOS 5.3 (build 16U5566a) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-07-09T17:19:30Z. The update package is 451.66 MB. This is a delta (partial) update that requires 5.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 4976f40ed2ae5e67a9915dc7cedb75e6b7747189.zip.