watchOS 5.3 (build 16U5545c) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-06-11T17:13:19Z. The update package is 137.42 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: 521d91eaffa39cb3569bf61d45a5359afdc26d28.zip.