watchOS 5.2.1 (build 16U5110a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-04-29T17:38:45Z. The update package is 497.12 MB. This is a delta (partial) update that requires 5.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 83723be7715391b2d76583cd649968b933c61708.zip.