why is my touch screen is not working

Restart your iPhone or iPad. Make sure that your screen is clean and free of any debris or water. Disconnect any Lightning or USB-C accessories. If your screen works after removing an accessory, try using a different outlet, cable, or charger.

If the screen isn't working on your iPhone or iPad - Apple ...

First, force-restart your phone:

• Press and quickly release VOLUME UP
• Press and quickly release VOLUME DOWN
• Hold the SIDE button until an Apple logo appears (15-30 seconds), ignoring "slide to power off" if it appears

The operative word here is QUICKLY; and try it a couple of times, the timing is a little tricky.

If that doesn’t fix it make an appointment to get the screen replaced→Genius Bar Reservation and Apple Support Options - Apple