The cover slide for a Module can be set in the Arranger. To get to the Arranger, go to the Content tab in your Module and click on the Add and Arrange Content button.
Next, select the slide you wish to set as the Cover Slide and click on the See Slide Detail button.
Finally, click on the Set Cover Slide button.
Your selected slide will now appear as the default cover slide in the Trainee's dashboard view.
The Course cover slide will be determined by the first Module in the Course.