Move your curser over your new guide step image, then click the Edit button in the bottom right corner.

Select the Markers option from the menu that appears to open the Markup Window.

Use the Tool menu at the top left to select a shape, line or arrow marker, then simply click the image where you'd like to add the marker and adjust the size, shape and orientation as needed.

Use the Color menu at the top right to select a color for your new marker.

Once you've created all desired markers, click the Save Changes button in the very top right corner of the Markup Window.

View your new image with the markup and click Save to save it to your guide step.