Sub Demo()
Application.ScreenUpdating = False
Dim strTmp As String, Sctn As Section, oCel As Cell, rngTmp As Range, i As Integer
With ActiveDocument
  For Each Sctn In .Sections
    With Sctn.Range
      If .ContentControls.Count > 0 Then
        strTmp = .ContentControls(1).Range.Text
        For i = 2 To .ContentControls.Count
          strTmp = strTmp & ":" & .ContentControls(i).Range.Text
        Next i
        With ActiveDocument
          For Each oCel In .Tables(1).Range.Cells
            Set rngTmp = oCel.Range
            rngTmp.End = rngTmp.End - 1
            If rngTmp.Text = vbNullString Then
              .Indexes.MarkEntry Range:=rngTmp, Entry:=strTmp, _
                CrossReference:="", CrossReferenceAutoText:="", _
                BookmarkName:="", Bold:=False, Italic:=False
              Exit For
            End If
          Next oCel
        End With
      End If
    End With
  Next Sctn
End With
Set rngTmp = Nothing
Application.ScreenUpdating = True
End Sub