@sunny
Thank you for your patience throughout this issue. I received an update from our engineering team and have done some testing on my end and will post my findings below.
Engineering team update:
You need a custom policy which targets rewriting the "strongAuthenticationEmailAddress" attribute
StackOverflow related question
A B2C IEF Custom Policy which uses Usernames as the sign in identifier
Get started with custom policies in Azure Active Directory B2C
Testing:
I tested out some alternative ways to reset a user's email and found that you can also do this by having the user go to:
aka.ms/ssprsetup
Once logged in, you can have a user change their email address or phone number, and this will update the "Authentication Methods" blade for the user.
You also have to ensure that you have "Email" checked under "methods available to the user". This is regardless of the "Number of methods required..", it can be set to 1 or 2.
Changed my email just to demonstrate:
Lastly, you can also easily change a user's Alternate Email address by using Msol commands.
Please let me know if you have any other questions.
Thank you for your time and patience throughout this issue!