There are a couple of options to filter out the junk from your Yahoo account without any issue. If you are looking to block a few terms such as promotion or deal, you can these words in the spam filter on your Yahoo mail .
If not, then you can use the report option on Yahoo mail to mark as spam and never receive another communication from them again.
To stop yahoo spam emails, you need to change the filter settings and make it more tough for advertisers to send you the bad stuff. However, if you are looking to just block someone, you can do that right from the mail. Just go to Yahoo Security and Privacy Settings and add an email address to block them from sending a mail in your inbox. It will go directly to the spam folder and you won't be bothered.
Also read - https://americanarticle.org/how-do-i-change-my-spam-filter-settings-on-yahoo/