To restore the iPhone when your apps are error, you often use iTunes to do this, but 3uTools app has the same function to restore iPhone as iTunes, the work is much simpler.
To restore your iPhone, follow these steps:
Step 1: Download the latest version of 3uTools
Step 2: Open the application on >> select Flash & JB.
Step 3: In this section, there will be the firmware that Apple has not locked activation, if you have downloaded the firmware before then you select Import.
Select the version to restore >> Open.
If you do not download click Download >> After done you press flash.
Hit Flash button
Step 4: The application will display % of the process of restore, you wait until 100% is done.
Step 5: Complete.
So I just guide you how to restore your iPhone. Good luck.
Note: This is a 3rd party application, so when you manipulate the considerations carefully. During the restore process you are not unplugged, do not turn off 3uTools. Also, you need to leave your iCloud account before doing so to avoid undesirable conditions.