Restart Your iPhone

If your iPhone still feels like something is wrong, restarting it is a quick and easy solution. Yes, we’ve all heard that you should turn off and back on your smartphone, but there’s a reason why they tell you this.
 
Restarting your iPhone will clear its RAM and end background processes. Afterward, your iPhone will start the processes from the beginning, which will hopefully get rid of any temporary bugs you experienced. 

To restart an iPhone with Face ID, press and hold one of the volume buttons and the side button simultaneously. For an iPhone with Touch ID, press and hold the side button.

Wait a few seconds and then swipe the Power Off slider to the right. After waiting a few seconds, press and hold the side button to turn your iPhone back on again.