As you send a campaign to a list or lists, the status bar next to the list indicates the list progress.
Once the progress bar reaches 100%, to send to that same list again you will have to flash the list before sending your campaign.
You have two options to do so;
From Campaign - go to the campaign, click on black “tester” icon, click on lists sections and click on the "START OVER" icon on the right.
2. From List - go to lists, select the list and click on the START OVER icon
Hope this was useful
Happy sending