You may try a force restart to see if it works, follow the step-by-step guide:
* Press and hold '''HOME + POWER''' button for '''10 seconds''' and then release the buttons. You will see that your '''screen turns OFF'''.
* No again press and hold '''HOME + POWER''' button again for '''8 seconds''' until you see '''Apple Logo''' and then release the buttons after the '''iPhone screen turns OFF'''.
* Now again press and hold, '''HOME + POWER''' button for '''20 seconds''', then only '''release the POWER''' button and still '''hold the HOME''' button.
* After '''20 seconds''', release the '''HOME button''' and your iPhone X/8/8 Plus shall start in normal mode as usual.
Hope this info helps you!