watchOS 5.3 (build 16U5545c) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2019-06-11T17:13:40Z. The update package is 182.51 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: f492a332f9c263b88fb07001fca063bb91c98582.zip.