Thank you for your feedback.
To change the sending name in Yahoo Mail, please follow these instructions:
Please note: Some third-party apps have their own sending name setting, which bypasses the Yahoo Mail setting. If the app you're using attaches a different name than the one saved in your Yahoo Mail settings, contact the manufacturer of the app for assistance.
Yahoo Support Team
An error occurred while saving the commentFiona Graham commented
Me too. Sooo annoying!