watchOS 5.2.1 (build 16U113) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-05-13T17:16:06Z. The update package is 994.16 MB. This is a delta (partial) update that requires 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: d9309f1c4b6953d022b7c99636207f9a0867e85d.zip.