The location ID refers the the ID generated by Sears when you first created your fulfillment locations. Visit Account Settings>Fulfillment locations and you will be able to see what the ID is for each of your Warehouse and Pickup locations. You can also edit this number (for example you may want to use your store number for the pickup locations).
When submitting your inventory be sure to specify the inventory quantity available for each of your locations (warehouse and pickup).
Please see the sample inventory template attached below.