There are many reasons why you might want to edit or update your sequence once your campaign is published.
You can edit a sequence by clicking show more button indicated by the three dots and selecting Edit Sequence from the drop-down menu, which will open the sequence editor where you can make changes to your sequence.
Changes can only be made to the sequence, and not the audience. If you'd need to make changes to the audience, you'll need to duplicate the campaign to update the target audience. You can duplicate the campaign from the drop-down menu.
Once you're done editing the sequence, save and publish.