iphone 8 plus home button

[oppland]

I just received a used iphone 8 plus and the home button works, but it looks like it's missing the round (cover?) I've attached a pic.

Does anyone know what that is called, and if I can fix it?

If it was for me it would be fine, but it's for my son and I'm sure he could turn this into trouble somehow.

 

[now i see it]

That phone doesn’t have a physical button. Just a thinner covering where the mechanical button on the older phones used to sit.
I believe the front screen has to be replaced to fix what you’re looking at.

 

[BugeyeSTI]

Home button is matched/married to the logic board in your device, replacing it will disable TouchID and you'll have to unlock your device using the passcode. Apple can replace it and has the necessary software to complete the repair properly