How do I delete open apps on an iphone sx

Swipe from the bottom of the screen to the middle and pause,l then take your finger off the screen. This should bring up the App switcher, and you can swipe the apps up and off the screen to close them.

This however should not be necessary in normal usage unless the App has stopped responding or is behaving strangely.

More details here: How to force an app to close on your iPhone, iPad, or iPod touch - Apple Support

See this > How to delete apps on your iPhone, iPad, and iPod touch - Apple Support

Wow, did I misread your question, my apologies.