Apple releases new iOS firmware that makes it temporarily impossible to take advantage of unauthorised features available through jailbreaking your device. You may need to revert to an older version to jailbreak again.
Backup your device. Having a backup will help minimize any downtime if the downgrade process doesn’t go well. See this guide for instructions on how to backup your iPhone.
Download the 7.1.2 IPSW file. An IPSW file is the firmware file that contains the iOS system software. You will need to download the signed IPSW file for 7.1.2 that is specific to your device. There are different files for different phones and different carriers.You can find the IPSW files at places like iDownloadBlog.com
Select your device and click the Summary tab.
Load the IPSW file. Hold down ⌥ Opt (Mac) or ⇧ Shift (Windows) and click Update. Browse for the IPSW file that you downloaded.
Setup your device. After downgrading, your iDevice will show the Setup screen. Follow the prompts to setup the device.