iOS 13.3.1 (build 17D5026c) is an official Apple over-the-air update for the iPhone 6s+, released on 2019-12-17T18:13:32Z. The update package is 193.58 MB. This is a delta (partial) update that requires 13.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: f6619d38cbf507cc8d65f2244ff7a9e80e968b16.zip.