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 164.75 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: 206adbcfe9f3c718a7f73ed74c0539f550ec1daa.zip.