If you just want a backup and haven't lost anything do the following.
Install and open Terminal Emulator, and enter this:
That's it! The phone will reboot and create an on-device backup. You don't have to ever do it again as its not wiped by recovery or Odin flashes.
In the event of imei loss enter this to restore:
Credit to docholiday
Sent from my SGH-T999 using Tapatalk
Samsung Galaxy S 3|SGH-T999
Kernel: KT747 3.0.31
Rom: Dandroid 5.2
Multiboot ROM: CM11