How to re-subscribe records who are already unsubscribed.
Solution
Once the person is willing to resubscribe to receive your emails, either of the following can be done:
Smart Campaign: Change Data Value of "unsubscribed" to false.You can either use a Smart Campaign to execute this flow or can just go with single flow action ( select the lead, Person actions > Marketing > Change Data value; Attribute: Unsubscribed, New Value: False.)
You can manually change unsubscribe from True to False. To do this, go to Lead database, click on the lead ( whom you need to unsubscribe), go to lead Info tab, look for unsubscribe field , remove the tick or check off the unsubscribe field checkbox.