Here's how you can use AssistiveTouch to turn off your iPhone.
1. Go to Settings.
2. Go to Accessibility.
3. Go to AssistiveTouch.
4. Toggle AssistiveTouch to the On position.
5. An on-screen home button will appear.
6. Tap the on-screen home button.
7. Tap and hold the Lock Screen icon. The "Slide to Power Off" option will appear to let you turn off your iPhone.
For more, see the original article at the link below.