Optional Action Planning allows you to add an action plan to a response without needing a trigger to create the task. If a submission's survey has tasks turned on, you will see a "Tasks" tab on your response page

If your response has automatically triggered a response, you will see it under the "Tasks" tab. If this survey has the Optional Action Planning applied, you will also see a "Add New Action Plan" button under the "Tasks" tab. Click this button to create a new action plan. Your new open task will appear in the table, use the open button to enter the task and complete your action planning.

Even Optional Action Plans must go through the approval process, so be sure to follow the same steps as a regular action plan. To learn more about those steps, check out this article on action planning.