iOS 11.1.2 is available for download right now, and it patches a bug that was causing iPhones to become unresponsive in cold weather.

How to update iOS device to iOS 11.1.2 using 3uTools?

You’re suggested to customized back up your iPhone first.

Step1: Connect your iDevice with USB cable to your PC and then launch the latest version of 3uTools. 

Step2: Go to "Flash & JB" -> "Easy Flash", select the firmware iOS 11.1.2. And then click "Flash". (If you want to save iDevice’s data, please select the checkbox "Retain User's Data While Flashing".)

Step3: 3uTools will automatically flash your iDevice, please wait patiently for around 5 to 10 minutes till the process finishes. 

iDevice will restart automatically after this process, then you can activate iDevice by manually or activate iDevice with 3uTools.