Chosen Solution
My screen went black and I want to repair it. I need to know how to power down the iphone with out a functioning screen, home button, or power button.
Your best bet is to open your phone, unscrew the 3. screws that secure your battery and charging port and unplug it. There isn’t a way to turn your phone off without functioning buttons.
Press and hold power and lock button until the apple logo appears :)