To edit an action within an Automation flow, you'll first want to click on the flow name in the Automations table. From there, you'll want to locate the Action Step that you are wanting to make changes to. Click on that step and you will see an email settings panel appear on the left side of the screen. 

Locate the edit icon within that panel and click on it to open the email editor for this specific action. Within the editor, be sure to enter a promotion code if the template calls for it (all promotion codes will be created within your specific shopping cart's platform) and add in any personalized elements like images. 

Once you are done editing, click on the save and exit button in the top right corner. Complete this steps for all actions within the flow and you will be ready to get that Automation Flow turned on!