1. Enter "Inventory" -> "Manage Inventory" -> Search for the sku you wish to adjust. Then click into the Sku's product page. 

2. Click "Product Warehouse. 

3. You will see a list of every warehouse on the next page, it will show how much is currently stocked into each location. Scroll down slightly, you will see "Adjust Inventory", "Transfer Inventory" and "Set Physical Inventory". Click on "Adjust Inventory" to expand the section. 

4, Once you have expanded the section, you need to select Warehouse (most used is WH-FL), fill in the qty to adjust (if you want to add one just type "1", if you want to remove one just type "-1", select the appropriate adjustment reason (for this solution - "product disassembly for parts"). Finally hit Save Adjustment.