Update email with a custom email template in Firebase

Question

I have a Flutter mobile application and I am using Firebase authentication. I have decided to use email template for verifying user email. In the backend, I call generateEmailVerificationLink(email ,actionCode) to create an email verification link, then I pass the link to a good looking email template and send it to the user.

I would like to do the same thing for updating user email. But I am not sure which function to call in the backend to create the proper link that I need to pass to the email temple. The mode in the action code should be "verifyAndChangeEmail"

Does any one know?
I found this link https://firebase.google.com/docs/auth/admin/email-action-links but it does not say how to generate a link for updating user email. Does that mean that I can't have a custom email for updating user email?? Please help.