Although an iPhone comes with Safari as the default web browser, you can download and install the Yahoo Mail app on the iPhone and change Yahoo password. For this, login into your Yahoo mail via Yahoo Mail app. Now, tap on the "Manage Accounts" through the "Menu" icon. Then, tap on "Account info" and then "Security Settings." Now, enter the security code for your iPhone and then tap on "Change Password." Now, enter the new password twice to confirm.

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