From your referral or leads page, you may hide candidates who you think are irrelevant for current or future roles, to keep your Intrro environment up to date with the most suitable candidates at all times.
When you complete this action, they will no longer appear in your candidate pool, but can easily be recovered from your Settings tab.
Navigate to Personal Settings and under Personal Information, you can find the tab Recover Candidates, where you have the option to reinstate them back to your talent pool on Intrro.