Once contacts have been added to Agent Legend, you can easily send them to a new campaign to reengage them. From the Contact List page, select the contact by clicking the top corner of the lead tile. Then, click the "Add to Campaign" button to select the campaign you'd like to add them to:
Note: Adding too many contacts to a campaign at once in this fashion may cause you to go over the limit of 200 contacts per 24 hour period. This article goes over those limits.