Go to Clients >> All Clients >> Click on the eye icon against the client >> Exclusion List tab. You would be able to find the list of candidates added to the exclusion list.
If required, you can add more candidates by clicking on the Add button.
When you click on Add, you will get the window below. Choose the candidate, enter the reason and click Submit.
Note: When a candidate is added in the Exclusion list for a client, their name won't come up in the available candidate list of any job for that particular client until they are removed from the list.
Once you have added a candidate to an exclusion list, the list of clients that have them in the Exclusion list can also be seen on their profile >> Exclusion List tab as shown below.