On the menu bar, click Evidence, then click Citizen Evidence, and then click the View Summary link for the portal you want to close. The Portal Details page opens.
Under the Share Public Link heading, toggle the switch to say Closed for Submissions.
This closes the portal and the link is no longer active. If someone clicks the link, they will get a Page Not Found message in their browser. The portal can be re-opened later by toggling the switch.