Begin by going to Excursions / Trips located within the Scuba Diving feature on the tree menu. Trips are not automatically moved over to the Historical Excursion view. This allows for payments to be made after the trip has ended.

To close a trip you must first click the Enter Edit Mode icon in the toolbar. This will make the trip selected in the Excursions & Trips window editable. The Close Trip column is the very last column, which you can get to by using the scroll bar at the bottom of the window.

Select the excursion you want to close and check the Close Trip box. Click the Save icon in the toolbar to commit the change and then click the Leave Edit Mode icon in the toolbar. The closed trip will be in the Historical Excursions view, accessed by clicking that icon in the toolbar. (The current excursions list will not be refreshed until you move off of it by going to Historical Excursions or the next time you open the Current Excursions list view).