watchOS 5.3.9 (build 16U693) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2020-12-14T18:09:00Z. The update package is 133.42 MB. This is a delta (partial) update that requires 5.2 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 4bd463293c27784b01fd1124ee531053f4b3c168.zip.