There are two ways you can add the unsubscribe link to your Email Marketing:
(1) Add a Footer to your Email Marketing - the Footer content block comes pre-populated with your Organization's contact information (from your Organization's Profile) and an unsubscribe link.
(2) Use the unsubscribe code - you can also use the unsubscribe link code to create your own unsubscribe link.
Select the text and click the Add Link Button
Add the code {{unsublink}} in the URL field with the Text of your choice