From most Yahoo mobile apps:
1. Tap the Menu icon.
2. If using the Yahoo Mail app, tap Manage Accounts.
3. Tap Account info.
4. Tap Security settings.
5. Enter your security code.
6. Tap Change password.
7. Tap I would rather change my password.
8. Enter the new password and its confirmation and tap Continue.
Or Dial Our
Yahoo Mail Customer Service Number
Yahoo Customer Support Number