Is to head to where you get those ROMs and I'm sure they cover how to flash back to stock and recover from bricked devices.
If that's not an option, ask Samsung how much to repair.
Hi.I have a big problem
I am custom rom user and use Enigma Rom for J7(SM-J700F).Recently i flashed "Speed fusion Remix ROM" but i didn't liked it so i decided to go back to Enigma ROM V5 but no phone stuck on boot animation and vibrates after every 10\20 seconds.I also tried to flash Stock ROM via odin and it is also saying failed on now i can install Speed Fusion Remix ROM i want ENIGMA ROM V5 please help me.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic