hiow do you soft reset the iPhone X

A soft reset is basically just turning it off: you can go to Settings > General scroll to the bottom tap shut down and then slide to shut down. If you want to do a forced restart press the volume up button and release it, press the volume down button and release it then hold the side button in until you see the Apple logo then release it.

See "If your screen is black or frozen" here:

If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support