How to remove the gray icon that's for the control center

If you bring Control Center up from the bottom of the screen, dismissing it can be done either by tapping on the Home button, or you can swipe it downwards again from the top of Control Center and it will go back down. However, reading your reply again sounds almost like you are referring to the Accessibility control called Assistive Touch. This puts a button on the screen that can be programmed to perform some functions of the home button, etc. To dismiss that, you need to go to Settings>General>Accessibility>Assistive Touch>OFF.

You're welcome. Glad I could help. 🙂