Select the order in Awaiting Assigning tab
Edit its quantity by clicking on edit
Then check Reduce Quantity and then click ok button
By reducing quantity to 0 then click on tick icon and then update items button
Order will move to Edited by EBM tab and only users having access can update it
Select the order and then click update button
Product will be removed from order and updated order will move back to awaiting assigning tab, awaiting approval tab.