By default, SharePoint designer will automatically select an existing Task list ( The one created along with the template) or create a new one if a suitable Task list does not exist. To change the Task list used follow these steps.
- Create a new Task list using Site Actions + Create.
- Find the Id (Guid) for this new list (From the address bar of the list’s settings page)
- Using SharePoint Designer, open the site where the workflow exists, expand out the “Workflows” folder and the workflow whose Task list is to be changed.
- Locate the file called workflowname.xoml.wfconfig.xml and open this file for editing.
- Take the GUID of the list you found and replace the Id in the “<Association>” element’s “TaskListID” attribute.
- Save the file.