Procedure is the same like when you convert 37xx to 34xx

remove gupdate.gcd from .System folder

rename text, keyboard, voice folder to something else

clear non vol

Download rgn below

[Only registered and activated users can see links. ]

drag and drop on updater.exe and flash

p.s.
if you stuck on black screen you must find spot on screen for enter pre boot to flash back to 34xx ( above letter G, but you dont see G you must press screen on blinde)