watchOS 5.3 (build 16U5545c) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-06-11T17:13:33Z. The update package is 92.22 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: b8471ef9827a5a92fad925714d49914f61dedcb3.zip.