To block all the results from a specific source, click on:
Edit query > Sources > Turn off sources you wish to block mentions from...
(Certain source is turned off when the button next to its name is grey)
If you wish to block certain Website, Facebook profile, Twitter profile, etc., follow the next steps:
Example of blocking a certain website:
Edit query > Sources > Websites (click on a drop-down list) > All websites except... (write domain of the website you wish to block)
If you choose to edit the query, we would advise making sure you extracted your data in a form of a document or report prior to making a change because by editing the query you're restarting the search.