如何在不同方法中编辑arraylist中的修改对象

I want to be able to modify the different attributes of the elements that are stored within my array list called list. However, I need to be able to do this within my sell command. For example I would want to accept in the sell method the name of the item and the amount that user would want to sell. Then I would need to set within the sell command the new quantity I believe. I am coming up short on how to edit anything on the array list within the new method. Any help would be great.I want to be able to modify the different attri