The order of events in a campaign cannot be altered once the campaign is published. To make changes to your campaign, unpublish it first and then make your changes. This article details how to edit your email campaigns.
If the email campaign has already started going out to recipients, you will not be able to unpublish it. You will need to pause the campaign, then duplicate it to make any changes.
If you would like to "resume" the campaign for the accounts who have already received emails, we recommend following these steps:
1) Unpublish the campaign you are hoping to edit.
2) Duplicate the campaign.
3) Delete the steps of the campaign that have already been delivered.
4) Make any necessary edits for future steps.
5) You can then publish the campaign and send it out to your list of accounts.