watchOS 5.3.5 (build 16U652) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2020-02-18T18:06:57Z. The update package is 47.06 MB. This is a delta (partial) update that requires 5.3.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c0ce9d9850cf779dd372636b3e091ecce1a1bc62.zip.