Can You Modify This Code To Search Only One Colomn?

Private Sub CommandButton1_Click()
Dim strFirstAddress As String
With Sheet1.UsedRange
Set rngFind = . Find(ComboBox1.Text, LookIn:=xlValues)
If Not rngFind Is Nothing Then
strFirstAddress = rngFind.Address
Do
rngFind.EntireRow.Copy sheet3. Range("a" & sheet3.Rows.Count).End(xlUp).Offset(1, 0)
Set rngFind = .FindNext(rngFind)
Loop While Not rngFind Is Nothing And rngFind.Address <> strFirstAddress
End If
End With
Unload UserForm2
UserForm4.Show
End Sub

The problem is it searches the whole sheet, what I want it to do is only search one colomn (colomn A). I know its prob an esay thing to change but I can't for the life of me do it!