I'm not running the beta of iOS 13, so perhaps it is different, but in iOS 12 you can swipe up from the very bottom of the screen and then hold your finger down a moment longer before lifting. This will bring up the multi-tasking control that shows all of your recently used apps in a 'card deck' kind of display. You can scroll right or left through the apps with swipes right or left; you can 'purge' apps from the display by flicking them from the center upward. Supposedly purging an app in this fashion will kick it out of memory (and free up its memory). However, I agree with Loki that in modern versions of iOS I've never seen much point in clearing out apps this way.