To restart an app on an iOS device you first need to shut it down by double pressing the Home button and then swipe the app up so it disappers from the list. After this return to the Home screen and start the app again and it will now make a fresh start.
Make sure you’re on the Home screen and then press the “rectangle” button on the bottom of the device. It’s typically located to the right of the devices Home button. A list of recent apps will appear and then swipe the app to be off the screen (left or right) so it disappears from the list. After this start the app again.
On some devices the Home button has to held down a short while to make the list of recent apps appear.