Sub Macro1()
Dim oTable As Table
Dim lngCount As Long
Dim i As Long
    lngCount = ActiveDocument.Tables.Count
    For i = lngCount - 2 To lngCount 'process last three tables
        Set oTable = ActiveDocument.Tables(i)
        'do something with oTable e.g.
        oTable.Cell(1, 1).Range.Text = "This is cell 1"
    Next i
    Set oTable = Nothing
End Sub

Sub Macro2()
Dim oRng As Range
Dim oTable As Table
    Set oRng = ActiveDocument.Range(Selection.Range.Start, ActiveDocument.Range.End)
    For Each oTable In oRng.Tables
        'do something with otable e.g.
        With oTable.Cell(1, 1).Range.Find
            .Text = "cell 1"
            .Replacement.Text = "the first cell"
            .Wrap = wdFindStop
            .Execute Replace:=wdReplaceAll
        End With
    Next oTable
    Set oTable = Nothing
    Set oRng = Nothing
End Sub