What you will need:
An email campaign that's either a Simple Schedule, RSS, or Scheduled before the next execution date.
Step 1:
Click on the pencil icon next to the campaign
Step 2:
You will be able to make changes to the details of the email like changing the elements or words
Once the changes are made, save the edits
Step 3:
Select the Send or Schedule button to reschedule or change email recipients