Literalmente, o que você quer se traduz em algo como isto no módulo de planilha para a folha 1 -
Sub worksheet_change(ByVal target As Range)
Dim actdatex As Integer
Dim actdatey As Integer
Dim newcell As Range
Dim rngdate As Range
If Not Intersect(target, Range("A2:A999")) Is Nothing Then
On Error GoTo handler
For Each c In Range("Sheet3!C6:AK7")
If c = Worksheets("Sheet2").Range(target.Address) Then
actdatex = c.Column
Exit For
End If
Next
Set newcell = Range(target).Offset(, 4)
For Each d In Range("Sheet3!B20:B29")
If d = newcell Then
actdatey = d.Row
Exit For
End If
Next
Set rngdate = Cells(actdatex, actdatey)
rngdate = "X"
End If
handler:
MsgBox ("not found")
End Sub