How do I uninstall mirroring app? Is it hidden

You can't uninstall screen mirroring as it's built into iOS. But you also can't mirror unless you permit mirroring to a device which is compatible to mirror to. You can't mirror to another persons phone or iPad, for example. You can mirror to a compatible Smart TV, and even then only with a code to enter which you control if you want to use mirroring.

In other words, ONLY YOU can control mirroring from your phone to a compatible device, so you really don't have anything to worry about.

It sounds as if you're talking about AirPlay which is part of iOS. No one can mirror your phone to anything unless they have it in their hands unlocked. As it's part of iOS, you cannot remove it.

AirPlay - Apple

How to AirPlay video and mirror your device's screen - Apple Support