Clear app from cache:
To do this on iPhone 8 or lower,
Press twice on the home button quickly, this will show all of your open apps.
Scroll to the one you want to close, then swipe up.
Tap on the home button once again to get back to the home screen.
For iPhone X or higher,
Slide up from the bottom of the screen about a third of the way up the screen.
This will bring up the list of apps running in the background.
Scroll through to the app you want to clear and slide up.
Tap away from the other apps in the list to get back to the home screen.