1. Download the stock stable firmware from here :-
http://g3.letv.cn/194/4/13/letv-hdt....=5&splatid=500
2. After downloading the "S1_x500-OS-OP-DHXOSOP5500802191S-5.5.008S.zip" file, extract it to a folder on the PC.
3. Go to <Folder Name you gave>\META-INF\com\google\android
4. Open the updater-script file with Notepad(Notepad ++ preferable)
5. Rename all places where you find "X3_HK' TO "X3" ONLY.(DO NOT EDIT ANYTHING ELSE,JUST REMOVE THE "_HK")
6. Save the file.
7. Now again make a "zip" of all files you previously extracted. you can give any name to the zip file.(Including the META-INF folder you edited)
8. Paste this zip to ROOT of your internal storage.
9. Boot into TWRP Recovery, install this ZIP, And Voila!! It gets SUCCESSFULLY installed.