Download iOS 10.3.1 (14E304) for iPhone 6+

You will have to note that you can only restore signed IPSW firmware files using iTunes or 3utools.

❌ This IPSW firmware is not being Signed by Apple

Firmware Identifier iPhone7,1
iOS Version 10.3.1
Release Date 2017-04-03
Update Date 2017-04-01
Sha1sum
179925221cd2f34cdcea5034d9d7c211712ce661
Sha256sum
6636f2dccafda36410ecdf4c467cec753c4e2ccd29494566ff97789f386db88f
md5sum
915b5da280658a374d98b32529cd3a41
Size 2.58 GB
FileName
iPhone_5.5_10.3.1_14E304_Restore.ipsw
Status

Download IPSW (2.58GB) Check device info
Release Notes

It should be noted that these are the official release notes for the from Apple

iOS 10.3.1 includes bug fixes and improves the security of your iPhone or iPad.

For information on the security content of Apple software updates, please visit this website:

https://support.apple.com/HT201222