You may change the Stock group 1 and / or 2  for selected stock item(s). 

To change the Stock group 1: 

1.On the Action ribbon, select Stock items.

2.Select the stock item(s), right-click on "Stock group 1" or "Stock group 2" context menu. 

If you need to select multiple stock items, press the Ctrl or Shift key and click on each stock item, for which you need to change the stock reporting group.

3.Select "Empty" or the available Stock group from the sub-menu. The "Stock group 1" or "Stock group 2" will change on the reports.