Update your "Sending Name" on a mobile device
A Sending Name is the name your recipients see when you send email. Yahoo Mail uses 1 Sending Name per Yahoo ID.
Update it from a computer
A Sending Name can only be changed from a desktop computer. Once your name is updated on a computer, it's also adjusted on your Yahoo Mail app.
Does your mobile device have a different Sending Name?
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.