watchOS 5.3.9 (build 16U693) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2020-12-14T18:08:43Z. The update package is 467.01 MB. This is a delta (partial) update that requires 5.1 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: d9aca91d30174fb62da1663e991d9beac8059f5c.zip.