Thank you for posting this in Microsoft Q&A.
I understand that you would like to add a "Change Your Password" button for users signed into Entra External ID. If my understanding of the issue is incorrect, feel free to post back.
In B2C tenant if a user knows their password and wants to change it, we can use a password change flow. A user can change their password by using the self-service password reset flow if they forget their password and want to reset it.
But in external tenant we have the self-service password reset flow where users reset or change their password. With the help of 'forgot password' feature already authenticated user can be able to reset/change the password in Entra External ID. This option becomes available during the sign-in process. Instead of the forgot password text, you can change the text to 'Change your password' with the help of the password collection display text.
For more information: To customize self-service password reset
As indicated in the documentation, it is possible to disable the Show Self-Service Password Reset (SSPR) feature and replace the default URL with a common one. However, if SSPR is disabled, users will not be able to reset their passwords or see the 'Forgot' option on the sign-in page. The common URL value will only be working on the sign-in page if the SSPR option is enabled.
Hope this helps. Do let us know if you any further queries.
Thanks,
Navya.
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