iPhone 7 won’t turn on

My sisters iPhone 7 Plus had a accessory not supported message stuck on her screen. Would not disappear after pressing the ok button. I tried turning it off but could not slide the power off so I instead soft reset it. Now it does not turn on nor detect charging. I have also tried connecting to a computer with no luck. I have cleaned the lightning port and still nothing. If anyone has a answer for this please let me know.