Head on over to Marketing then into Campaign Report.
Specify your date range for when the Campaign was sent, and locate the Campaign that you're looking to re-send.
Once you've clicked Re-Send, you need to choose if you want to to re-send the campaign to everyone, or to failed recipients only.
If you want to re-send it to everyone on this campaign list, click All Recipients.
If you want to re-send it to client's with messages that failed/had an error, click Failed Recipients Only.
If you have any questions, please let us know via the Submit a Request option in your Help & Support page.