To restrict the candidate from a business unit, click on the candidate name from candidate list page

Once you click on the name, it will take you to the detailed profile page of the candidate.

Click on the Restricted tab, you will see the name of all business unit from which the candidate has been restricted.

To restrict from new business unit, click on Add button at the right corner in blue.

Once you click on Add, the list of all business unit will appear. You need to tick the business unit name which you want the candidate to restrict from and click on save.