From the Data Format and Mime Types main window, click the name link of the data format you want to edit, or select it and click the Edit button: 
The Edit Data Format dialog box appears showing the General tab.
Click the Relationships tab.
Click the Assign button: 
Select To Item Type or To Request Type according to the type of assignment to want to make.
The Assign dialog box appears.
Select the product that owns the item or request type you want to assign from the Product Id list.
Select the item or request type you want to assign from the Item/Request Type Name list.
Click OK. You will be returned to the Edit Data Format dialog box.
Repeat steps 3, 4, and 5 for each item or request type you want to assign.
When you have finished, click OK.