Próbáld ki ezt:

Dim i As Integer
Dim k As Integer
Dim Kom
For i = 4 To 700
        For t = 4 To 128
            If Cells(i, t) = "M" Then
                Set Kom = Cells(i, t).Comment
                If Not Kom Is Nothing Then Cells(i, t) = Cells(i, t).Comment.Text
                Set Kom = Nothing
            End If
        Next t
Next i