Firstly, download a 11.0.5 or an earlier iTunes version. When you uninstall latest version, remove all services and traces like Bonjour, Apple Mobile Device, and Software Update.
After installing the latest version, restart computer before you download a lower iTunes version. Delete the “iTunes Music Library.xml” file if you come across any error when downloading previous version.
Now, you should download iFaith’s latest version and also iOs 6.1.2 or 6.1.2 firmware. Now you should launch the iFaith and hit the ‘Build “*signed* IPSW w / Blobs” icon. This will start the custom firmware process. When you are prompted, choose the SHSH blobs. iFaith will then start creating a downgradable iOs 6 firmware file which you want for your iPhone.
Once iFaith ahs created the firmware file, follow the instructions online to put your handset in Pwned DFU mode. When the device enters this mode, launch the iTunes and choose your iphone and keep holding down the left SHIFT key and then click Restore iPhone. Now navigate to the custom firmware file that iFaith created. Your device will now be running on iOs 6.