How do I reset the monitor art. 7539?

Reset procedure: 1_ press and hold down the Speakerphone button; 2_ At the same time press the Self-start button and hold down until the Bell button starts to flash. 3_ Release the buttons; 4_Press and hold down the Self-start button until a long acoustic signal is heard. 5_ During the acoustic signal, release the Self-start button and press the Lock button. 6_ Release the Lock button.