If you can't log into the yahoo mail account because of the incorrect username or password error. That means, your password has been expired or someone has changed the login details. So here are the guide to fix the problem.
1. First of all, you need to reset the password for your yahoo mail account.
2. Now update it on your mail application. if you are using the auto login settings, you need to update it on your browser as well.
3. Update the yahoo mail account details. make sure that it is working perfectly fine.
once you will make these changes into the yahoo mail account, you need to visit down reporter blogs.