Please follow the below instructions to " Resubscribe"

 

1. Please click on  contacts. 

2. Please apply the filter  "Email is and enter the email address of the contact"

3. Please  select the contact once it is listed

4. Please click on  bulk action and select  Resubscribe and  click OK.  It will send an email with the button "Confirm   Subscription" The user needs to click on that button and he will be resubscribed.