The message icon on my iphone has disappeared. How do I restore it?

I had the same problem. The icon reappeared after restart.

settings - general - reset - reset home screen layout. or look in your apps folders to see if it was placed in there

impossible to dissapear since its a static app.

try looking for it. swipe to the left to go to the next screen to see if it moved.

otherwise reset your home screen layout (Settings > General > Reset > Reset home screen layout)

I checked and did resetting, but its not coming

I did, But nothing happened