Default [Q] 3G not working

How to fix 3g? I am using Z919 ROM 4.1.2.... I like that ROM but 3g doesn't works. Which files I have to replace using stock ROM? Can anyone help please.
Device: Samsung Galaxy SIII GT-I9300
ROM: Stock Rooted
Android Version: Jelly Bean 4.3
Kernel: Boeffla Kernel 5.3