In Aurora click on the Cosmos button. If you have to choose the game first then select the game from the list. Should be one of the first items and click on OK.

Then at the right side in the "Value" field enter the quantity of the item. Change "Value Type" to "Byte". Click on "First Scan". Then change your quantity ingame somehow. Enter the new quantity in "Value" field again and press "Next Scan". Do that until there is only 1 item in the list on the left. Select and right => add to address list. Then in the bottom list double click the value in "Value" column to change it.