Default [Q] Stuck in recovery please help!

Hey guys my brother messed with his phone last night and he couldn't get it out of recovery. he was running on an s4 ROM with his S3 and when he tried to instal a cynogenmod ROM it failed & now he cant get out of recovery. Rebooting system just brings him back to CWM over and over again. Can anyone tell me how to fix this? He cant mount/storage

I'm guessing he'll have to flash the stock ROM through odin? But i don't know how to find the right firmware from sammobile. His FCC ID is A3LGTi9300A abd tge SSN is i9300GSMH. Can anyone please advice on this? He really needs his phone in 12 hours.. Thanks!