When you add additional steps at the end of a campaign that has already completed its cycle, you will need to select the contacts in the campaign and re-add them after adding the additional steps.
Step 1: Add the contacts to a project
Doing this will enable you to manage the contacts without remembering them individually.
Step 2: View the Project
Step 3: Edit the Campaign
Step 4: Re-Add the contacts to the Campaign
From the Project you created, re-add the contacts to the campaign.