watchOS 5.3 (build 16U5558b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-06-24T17:25:02Z. The update package is 220.12 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: 62158bb2120a902ebbff66d77ddd516ab2dc2c6f.zip.