Function GoToMyHeading(str As String)
  Dim doc As Document
  Dim vHeadings As Variant
  Dim v As Variant
  Dim i As Integer
  
  Set doc = ActiveDocument
  vHeadings = doc.GetCrossReferenceItems(wdRefTypeHeading)
  i = 0
  
  For Each v In vHeadings
    i = i + 1
    If InStr(v, str) > 0 Then
      Selection.GoTo What:=wdGoToHeading, Which:=wdGoToAbsolute, Count:=i
      Exit Function
    End If
  Next v
  
  MsgBox "Couldn't find the heading containing: " & str
End Function

Sub GoToMyHeading_Test()
  GoToMyHeading "3.2.1"
End Sub