How to force close an app (iPhone)

iPhone X

1. On an iPhone X or later or an iPad with iOS 12, from the Home screen, swipe up from the bottom of the screen and pause slightly in the middle of the screen. On an iPhone 8 or earlier, double-click the Home button to show your most recently used apps
2. Swipe right or left to find the Hello Heart app
3. Swipe up on the app's preview to close the app. 

iPhone 8 or earlier

1. Double-click the Home button to show your most recently used apps
2. Swipe right or left to find the app that you want to close.  
3. Swipe up on the app's preview to close the app.