Most of the work you do in the heap analyzer is accomplished through
  context-sensitive pop-up menus.  The menu item available on the
  Do-not-use Type List is as follows:

      Action             Function
      ------             --------

      Use Type       Removes a segment type from the Do-not-use
                     Type List.

  For information on other heap analyzer screen locations and pop-up
  menus, click the 'On Context' menu item in the heap analyzer Help menu,
  then click the location of interest.

  For information on using the heap analyzer, see the 'On Window' menu
  item in the heap analyzer Help menu.