Bring back the cost register report you created in lesson 8 ( if it isn't visible, use menu command Reports Menu/Cost Register/Default).
Double-click on any occupied row in the report. The Cost Data Entry form will appear, showing that cost item. Make some changes to the cost data, then click on Save & Exit.
The line in the cost register for that cost item will be rewritten to show the new data. Any relevant totals and subtotals will also be rewritten.