Android Q

Okay, for some reason you want to unroot your phone or bring it back to stock. This is useful if you no longer like custom ROM’s or need to send your phone in for warranty purposes.

This process will take you down to a stock firmware of RC29. If you just leave the phone on, you should receive OTA (over the air) updates automatically within a couple of days, so there are no other files you need to install to update your phone. You should be good to send the phone back in with RC29 if you are doing this for warranty purposes though.

1. Get the original SPL for your phone.

2. Rename it to update.zip and flash it to your phone.
(To flash, copy update.zip to your SD card then boot up while holding the Home key. Press Alt+S after the recovery screen loads to apply the update.zip file)

3. Download the DREAMING.nbh from the thread where you rooted your phone

4. Place DREAMING.nbh on the root of your SD card and start phone in bootloader (CAMERA + POWER)

5. Hit POWER to start the update DO NOT INTERRUPT!! I can not stress this enough!

6. Hit ACTION (push the trackball down) and your phone will reboot.

7. YOU NOW HAVE STOCK FIRMWARE, it will update on it’s own in a little bit.

NOTE: if you have flashed a custom splash screen to splash2 then you will need to erase that before step one with this code. Plug your phone into USB in fastboot mode.

Code:
fasboot erase splash2

After that you will have only one splash screen and when you flash the .nbh you will be fine.

Original source: tubaking182 on XDA Developers