“In this piece, we’ll discuss a few ways you can reboot your iOS device without using the Home or power buttons,” Bouchard writes. “Instead, you’ll utilize nothing more than the touch screen.”
“There are a few effective ways to reboot your non-jailbroken iPhone without using any buttons to do so,” Bouchard writes. “Probably the most convenient way to reboot your stock iPhone without using any buttons is with Assistive Touch. This is one of the only fast and convenient ways of doing so without any side effects.”
Easy instructions here.