To activate the first button you're going to need to got o this spot in the map
Look where my crosshair is to find the button, then shoot it to activate it

For the next step you're going to want to go here on the map
Look over to this building and shoot the button

For the final button you'll want to go here on the map
The button is directly under the face
Once you shoot the button the face will open up (It will look like it does in the picture) and the buttons behind you will float up and the "Hush Nau" will be there

I know its not a perfect guide but I hope it worked well enough to help you get the "Hush Nau"