When a new user logs in for the first time, they are allowed to change their password only if the administrator selected the "User must change password at next login" option during account creation.
If this option was not selected initially, or if the user has already logged in without changing their password, you can prompt them again by updating their user properties.
Simply disable and then re-enable the "User must change password at next login" setting. This will ensure the user is prompted to change their password the next time they log in.