SharePoint Designer is a great tool to customize and create Workflows. One of the common Actions which are used in WorkFlows is Create Item. And once you select that action, one has to basically specify the list where the action is performed. Sometimes when you create a new List in SharePoint it does not appear in the Create Item dropdown. You might try refreshing it, but it still does not appear.
In this case, what one can do is to close the SharePoint Designer Application using the X on the top right hand corner. And then re launch the Application. Now you would see the new list appearing in the Create Item DropDown 🙂 .