Open the PLC editor (double click the PLC or right click the PLC and open the editor). In the Task tab, click Program mapping.
In the dialog window, focus the programs to be added to a task.
In the left pane there are all programs available in a Solution, while the right pane contains programs which are already executed in the task. Clock OK to confirm changes. To save all changes to project, click the OK button in the red dialog.
Remember to upload the Solution to PLC to activate all changes.