iOS 13.3.1 (build 17D5050a) is an official Apple over-the-air update for the iPhone 6s, released on 2020-01-22T18:07:28Z. The update package is 164.57 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: 242fe7655fa4c779324ce0ba9f029984aaff1387.zip.