Here are the steps that you have to follow to block the Yahoo emails address.
On your PC and connect it with internet
Then go to Yahoo.com
Click on login and enter your email address
Then enter your password and click on login.
Click on security and privacy option under the settings>>More settings
Then click on add and enter your email address
Add the email and click on block/save
For more visit: https://emailspedia.com/how-to-block-emails-on-yahoo