How to remove mute check

Hi. If you mean Settings > General > Mute, this indicates that the side switch (above the volume buttons) works as a mute switch. You can unmute by moving the switch. Alternatively, you can select Lock Rotation for the switch instead of Mute. Then Mute will be available in Control Center.

Swipe upwards from the bottom of the screen to access the Control Panel. The Mute switch is there.