You can create a Destroy Object Action through an Activity Diagram or a Modeler pane.
To create a destroy object action through an activity diagram:
1. On the Activity Diagram toolbar, click the arrow in the split button that is to the right of the Accept Event Action button, click the Destroy Object Action button, and then on the Activity Diagram, click in free space or within an Activity Partition, Interruptible Activity Region or Structured Activity Node.
2. Type the name of the Destroy Object Action, and then press the Enter key.
Modeler creates the Destroy Object Action and on it creates the default Target Pin input pin.
To create a destroy object action through a Modeler pane:
1. In a Modeler pane, right-click the Activity or Structure Activity Node that is to own the Destroy Object Action, point to New, point to Action Node, and then click Destroy Object Action
2. Type the name of the Destroy Object Action, and then press the Enter key.
Modeler creates the Destroy Object Action and on it creates the default Target Pin input pin.
Accept Event Action button, click the 
Destroy Object Action button, and then on the Activity Diagram, click in free space or within an Activity Partition, Interruptible Activity Region or Structured Activity Node.