A fulfillment service is a third-party warehouse that prepares and ships your orders for you. Using a fulfillment service is an excellent option if you don't want to have to deal with shipping, or if you’ve grown beyond your existing warehousing capabilities to a point where you can't ship items manually anymore.
You can easily modify the location of your fulfillment service the following way:
Click on the DataFeed Manager,
Click on Product upload,
Open your task,
Click on Settings,
Under the Fulfillment Service option, please choose the one you wish to set
6. Scroll down and tick the Fulfillment Service option
7. Click on Save and Next at the bottom
Please note that if you modify this setting from "Manual" to any other value, you won't be able to modify the inventory locations.