watchOS 5.3 (build 16U5558b) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-06-24T17:24:57Z. The update package is 142.21 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: 65f17a4b643ec3275e8e4dd01b038c9427938c1c.zip.