how can I restore my iPhone X if the power button has broken?

Make an appointment at the nearest Apple Store to have the damage evaluated and your options explained.

I think they actually should take the good advice that frazzm737 gave them and get it serviced. Have you ever handled an iPhone with a broken side button?

The OP posted again in the iPhone Hardware forum and says the button is stuck in, which is what I thought: https://discussions.apple.com/thread/251659337

How will they be able to do a forced restart in the power button (side button) doesn't work?

Again, how would they do a forced restart if the side button doesn't work? You might want to edit that out this time.

"broken" might mean not working. So, don't take it so literally.

Try it out as a method to troubleshoot it - see if it works.

jdpotwin Said:

"how can I restore my iPhone X if the power button has broken?"

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Is it physically broken, or is it just not working?

A. If Physically Broken, Getting this Serviced:

• Apple Stores: Find a Store - Apple Support
• AASPs: Find Locations - Apple Authorized Service Providers - Apple Support
• Send-In Service:

1. Apple: would send you a box
2. You: would package it and send it to Apple
3. Apple: would fix it or replace it, if applicable
4. You: would receive it back from Apple

B. If Not Working:

If not working, well, then that is a whole different story.

Try this: Force restart iPhone - Apple Support

That is a silly statement. If it is not working, and it is quite easy for a user to determine that (often the spring fails). It is a literal statement, the user can't make it work when they push it.