While in the Action Plan  Manager, select your plan and in the “action Plan Details” window, click on “Manage Assigned contacts” 

Select the Action Plan under “Plan Name” 

Click on “Edit Action Tasks” 

In the “Script” column beside each of the task, click on the “Add Script” button to add a script

If there is a script added, this button will say “See Script”. Click to review or edit. 

Click “Save” to save your changes.