In order to be able to send emails through your Yahoo account from Manager, you need to follow these steps to generate password for Manager.
Go to Yahoo and click on Generate app password
In App passwords windows select Other app, then enter Manager app and click Generate button.
Yahoo will generate new password which you can save somewhere.
Then within Manager, go to Settings tab, then Email Settings and enter following information:
Hostname: smtp.mail.yahoo.com
Port: 587
Username: Your Yahoo Address (e.g. example@yahoo.com)
Password: Your generated password for Manager app
Sending Limits: 500 Emails a day or Emails to 100 connections a day.