I need to reset to stock firmware (4.3 mk2).
is there any way?
If you're talking about resetting on stock MK2 ROM, Settings > Accounts > Backup and reset (select "Factory data reset"). However, if you are running a custom ROM on MK2 baseband, it probably won't do what you want.
Note that this will essentially reset you phone to factory new, out-of-box configuration, but on Android 4.3, MK2 baseband.
I tried that but it just brings me to odin download mode