1) Get List of WorkItem:
witadmin listwitd /collection:http://XXXXXX/tfs/DefaultCollection /p:ProjectName
2) Export Specific WorkItem Type from the List:
witadmin exportwitd /collection:http://XXXXXX/tfs/DefaultCollection /p:ProjectName/f:C:\TFS\WorkItem\Product_Backlog_Item.xml /n:"Product Backlog Item"
3) Edit the xml in VS 2015 it will open Eork Item Editor
4) Add Custom Columns ( StartDate -- Custom.StartDate, End Date -- Custom.EndDate)
5) Set the Layout where the colum should display
6) Save the WorkItem Template
7) Validate the WorkItem template
witadmin importwitd /collection:http://XXXXXX/tfs/DefaultCollection /p:ProjectName/f:C:\TFS\WorkItem\Product_Backlog_Item.xml /v
8) Import the WorkItem template (by removing /v in previous command)
witadmin importwitd /collection:http://XXXXXX/tfs/DefaultCollection /p:ProjectName /f:C:\TFS\WorkItem\Product_Backlog_Item.xml
