iOS 13.3.1 (build 17D5044a) is an official Apple over-the-air update for the iPhone 6s+, released on 2020-01-14T18:21:12Z. The update package is 189.78 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: 25894a1dd6cc78156a89dda046a7e3ad7b71d4f7.zip.