Hi,
Did it happen out of nowhere? Or did it maybe happen after your phone got wet or something? Have you already tried restarting the phone by holding the power button for about 20 seconds? If your phone didn't get wet and the restart doesn't help, maybe the LCD connector got loose. It once happened to me with my one plus 2. You can click the connector back into place by following [guide|30611|this guide]. Check if the connector on the right is properly clicked into place.
Hope you found this helpful!