Typically, Apple discontinues signing older variants of iOS within days of the latest variant transportation. As I write this, it is still not impossible. But it might not be in the immediate future, if you are going to at all, so act now.
The very first trick is locating a copy of iOS 7.1.2 for your device. With chance, the iOS installer program you want is there.
So yours may be gone nevertheless, these programs are normally deleted by the Mac OS. Make sure you get the one which applies to your particular device.
Once it is been restored you are able to then click the Restore Backup button to place back your info and programs on the smartphone.