How do I force restart my Iphone

press and release both volume buttons and then hold down the power button for about 10 seconds.

To restart an iPhone, Press and hold the volume up, down button and then the power button until the Apple logo appears. This should take about 10 seconds.

For more details, see: https://support.apple.com/guide/iphone/force-restart-iphone-iph8903c3ee6/ios