watchOS 5.2.1 (build 16U5110a) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-04-29T17:38:43Z. The update package is 89.4 MB. This is a delta (partial) update that requires 5.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b978bc601fc2e5a9be521000dddebd95eb0d2967.zip.