You can use a short code for this. It is in the docs.
Allows a user to change their login code. The login code must meet the Login Code Complexity requirements defined on the Manager System | Telephony tab.
Details
Telephone Number: The user's current and new log in codes separated by a *, see the examples below.
Default Short Code:
Programmable Button Control:
Example
The user has a Login Code of 1234 and wants to change it to 5678. To use the short code below, the user must dial *60*1234*5678#.
Short Code: *60*N#
Telephone Number: N
Feature: Change Login Code.
Example
For a user with no login code currently set, they can still use the short code to set a login code. For example using the short code created above to set their login code to 1234 they should dial *60**1234#.
Example
System phone users can also use this short code to change the login code of an other user. For example 403 is configured as a system phone with a login code of 1234. User 410 has forgotten their login code and needs it changed. User 403 can do this by dialing the following:
*60*410*1234*<new code>#