If the User is using Speed Dial they would only need one Key for Speed Dialing.
So if Key Ten, or Key 23 on 3903/3904 Phones, the Speed Dial Key could have 25-100 Speed Dials 0-24/0-99. When the Speed Dial Key is pressed with Dial Tone, the Display will Say enter Two Digit Number. If 12345 is Key 01 and you Press 01 it will Dial 12345, If 07 is 9-1-800-XXX-XXXX, when you Press Speed Dial 07 it will Dial that number.
To change Speed Dial 01 from 12345 to 67890, With the Handset Down the user would Press Speed Call Button, 01 and new number and Press again to save.
If the user has more than one Key, they are using Auto Dial. Print the TN of the Phone and see what the keys are and what's programmed on the Keys.
If the user is using Auto Dial, You press the Auto Dial Button, enter the new number and Press Auto Dial to save, again Handset Down with no Dial Tone.
Good Luck,
L.A.CityTech