Once an Auto Attendant is created, it is possible to update the Menu Greeting by dialing an access code from any registered device. This is useful when the Auto Attendant message must be changed frequently (such as might be the case if a restaurant were to announce daily specials in an auto-attendant greeting).
In order to use this feature, you must know the access code to reach the desired greeting. Each greeting will have a different access code. To find the access code of a greeting, first Manage the menu prompt from the relevant auto-attendant configuration page as shown in the image below.
This will open a modal window showing details of the Menu Prompt. The access code is shown in the field labeled 'Star Code to Record'.

Dialing this star code from any device registered to the domain will allow you to record a new Menu Prompt greeting.