Use 3D screwdrivers and LCD sucker to open the iPhone 6S screen, and remove the iPhone display screen. Disconnect the iPhone battery, and then take out the iPhone 6S motherboard.
Fixed the iPhone 6S motherboard with a PCB holder fixture, put it under a Trinocular Microscope.
Apply some solder paste to U4500 IC, and then use hot air gun and Mechanic ESD tweezers to remove it. Clean the solder pas, and then solder the 4500 IC back the motherboard.
Connect the iPhone motherboard to the iPhone battery and iPhone display screen, and then use iPhone lightning cable to connect it to the computer, use iTunes to restore it again, now the iPhone 6S can be restored properly.
Enter the IOS system, test the functions on the iPhone 6S, all works normally, the iPhone 6S has been fixed.
I hope the above method will help you. If you have other more effective ways to resolve iTunes error 9, pls let us know in the comments section below.