Disable volume icon during app running

Hello, I am very new to this device development. I created a simple panorama presentation viewer and per client request, they rather use the control on the headset and not the hand controller.
I am working with Unreal and manage to create the functions using the volume buttons, but every time they are pressed the volume icon is displayed.
I don't know if I can disable that icon within Unreal? or I have to do something else.
Your help is very appreciated.
Fco.