Step 1 - User needs to go to the Inventory Module and by default after clicking on the inventory module user will be on the product page. Next user needs to find for the SKU in which user wants to enable the USN function.
Step 2 - Once user have search for the specific product user now can scroll to the extreme right and click on the edit option.
Step 3 - Once you have clicked on the edit option, product page will open. Now user needs to scroll down and look for Serialised Inventory Management and now user have the option to either enable Unique Serial Number or Serial/IMEI Number. And the Disable User can use the same Option