To find the first echo press the button on the side of the map in the Meriff’s office:

Press this button to find the first echo in Wiping the Slate in Borderlands: The Pre-Sequel

To find the second echo pull on the green books on the bookshelf:

Pull on these books to find the second echo in Wiping the Slate in Borderlands: The pre-Sequel!

To find the third echo press the button next to the gate. Then pull the lever of the slot machine.