When you forget your Yahoo password, you can reset it to regain access to your account. You can use your Yahoo password to access every Yahoo service you use. Despite the iPhone's default web browser being Safari, you can download and install the Yahoo Mail app so you can change the password. To change password Yahoo mail on iPhone, launch the Yahoo Mail app and enter the correct login credentials and tap on "Login." On the iPhone, tap the Menu icon and tap "Manage Accounts." Next, tap "Account Info" and then "Security Settings." After that, enter the security code for your iPhone, and then tap "Change Password." Then, tap on "I Would Rather Change My Password." Now, enter the new password and then enter it again to confirm.

See also - Why Is Yahoo Mail Not Updating , Yahoo mail not getting emails