You will have the choice to run the action on either a high or low resolution image. Before beginning crop your image into a square. Then run the action......it will stop to tell you to load an image or continue....you want to continue if you already have opened and cropped your image. When the little wedge appears use the transform handles that will appear to position the part of your image that you want to be incorporated into the design.
If you need help loading your action check out this link.