Select a topic from the list.
If you have admin privileges you can re-subscribe an unsunbscribed subscriber. This should only be used for testing unsubscribe functionality.
Go to your Subscribers ManagerThis is located here: Subscribers Manager
Find the Subscriber List containing the Subscriber you wish to resubscribeYou can use the Campaign drop down to navigate to each of your Campaigns, or Unassigned (those that have not been assigned to a specific Campaign), or choose "Show All". Alternatively you can use the Search input to search by Subscriber List name.
Click the List NameOnce you've found the list containing the subscriber you want to edit, click the List name. This is a link to a list of all subscribers within a particular list.
Locate the SubscriberUse the search input to type in the email address or name of the subscriber you're looking for.
Click the "Tools" button (a wrench icon)This will reveal a navigation drop down.
Click the Re-subscribe linkThis will completely resubscribe the user.