Kindly Reminder: Using this software, your iPhone will automatically install the latest iOS system, and will return to the non jailbreak state.
The following is a detailed description of the software, please read carefully.
Step 1. Choose the Repair iOS System feature
Go to the official website to download this software, and select "iOS System Recovery" from the function list. At the same time, use the data cable to connect your iPhone6 and computer. Then click "Start" to continue the process.
Step 2. Download and select firmware
Next you have to download the firmware, the software will automatically identify your phone model and recommend suitable for your phone firmware. You just need to click "Download" and wait.
The software will finish it for you automatically.
Step 3. Fix your iOS to return it to normal
When the download is complete, the software will automatically help you install the firmware, the recovery process may occur in the apple logo cycle, do not worry, this is a normal installation. The whole process takes less than ten minutes.
More info:
How to Repair iPhone That are Stuck in DFU Mode
How to Repair iPhone That Won't Turn On Without Losing Data