watchOS 5.3.9 (build 16U693) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2021-01-26T18:26:32Z. The update package is 470.14 MB. This is a delta (partial) update that requires 5.1.2 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: f4371b58f55708267407501580620f0d685db173.zip.