watchOS 5.3 (build 16U569) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-07-22T19:15:26Z. The update package is 177.55 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: 30ea9913c640fed51683a32876197161067f0910.zip.