For an iPad with Touch ID:
(1) Go to the home screen, then double-press the Home button (the only button on the front of your iPad) to bring up multitasking.
(2) Place your finger on the app preview screens, then do a swipe up gesture to quit each app. Each preview screen will slide up and disappear, indicating the app has quit, and the other apps will slide in from the left. Once they are all closed, press the Home button again to close multitasking.
(3) Next, do a cold reboot of the iPad by pressing and holding the On/Off button AND the Home button (at the same time) for 10+ seconds. Keep both buttons pressed, even when the screen goes black, only releasing the buttons when you see a white Apple icon.
For an iPad with Face ID:
(1 ) Go to the home screen, then swipe up from the bottom of the screen to bring up multitasking.
(2) Place your finger on the app preview screens, then do a swipe up gesture to quit each app. Each preview screen will slide up and disappear, indicating the app has quit, and the other apps will slide in from the left. Once they are all closed you will be returned to the home screen.
(3) Next, power off your iPad by pressing the Power button and the Volume Down button at the same time for a few seconds until the Slide To Power Off button appears, the slide the button to power off the device. After waiting a minute or two you can restart the iPad.
Here is an Apple support document with further details: https://support.apple.com/en-us/HT210631