Campaigns when completed are set to a status of Completed, or they can be marked as completed before they are finished (before all the messages have been sent). You can re-activate a campaign that has been completed by following the directions below. 

Go to the Campaigns page of BatchLeads by clicking the Campaigns button in the left navigation menu to view your campaigns. By default the view is filtered to show Active Campaigns. Change the dropdown filter option as shown below to show Completed campaigns to show your completed campaigns. 

You can use the search feature to find your campaign if needed. Then click the vertical dot menu by the campaign you wish to reactivate. Next select the menu option Remove As Completed. The campaign should should change to Active, and it should now appear under your Active campaigns.