watchOS 5.3.9 (build 16U693) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2020-12-14T18:08:57Z. The update package is 484.12 MB. This is a delta (partial) update that requires 5.0 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 622dac78fa465e01d4e69f04ff16f579b3fec3e9.zip.