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

To change the Stock group 1: 

  1. On the Default ribbon, select Stock items. Select the stock item(s), right-click on Stock group 1 or 2 context menu. 
  2. Select empty or the available Stock group from the sub-menu. The Stock group 1 or 2 will change on the reports.