How do you hard restart the iPhone 11?

Force Restart your iPhone exactly as shown below:

• Press and quickly release Volume UP button
• Press and quickly release Volume DOWN button
• Press and Hold the SIDE button until an Apple logo appears then release the Side button (Can take up to 20 seconds. DO NOT release Side Button when invited to Slide Power OFF).  

Axel F.

Force restart iPhone - Apple Support

you have 2 posts that tell you exactly how to do what you're asking..

What is happening when you try? Or.. What is the problem you are trying to solve?