code take more than 10 minutes to be executed - excel

Question

I use the following code to import text file tab delimiter, and use for loop for more than one million row, to modify some range("AF") with caller ID, but the problem it takes more than 10 minutes to finish and open the excel with the result.
So any suggestion to speed up the following code,
Public Function txtimport() As Integer
Dim b1 As Workbook, s As String, J As Long
Application.Calculation = xlCalculationManual
Application.ScreenUpdating = False
Application.DisplayStatusBar = False
Application.EnableEvents = False
s = Application.GetOpenFilename()
If s = "False" Then
txtimport = 1
GoTo Nofile
Else
txtimport = 0
End If
Close #1
Open s For Input As #1
J = 1
Workbooks.OpenText Filename:=s, Origin:= _
437, StartRow:=1, DataType:=xlDelimited, TextQualifier:=xlDoubleQuote, _
ConsecutiveDelimiter:=False, Tab:=True, Semicolon:=False, Comma:=False _
, Space:=False, Other:=False, FieldInfo:=Array(Array(1, 2), Array(2, 2), _
Array(3, 2), Array(4, 2), Array(5, 2), Array(6, 2), Array(7, 2), Array(8, 2), Array(9, 2), _
Array(10, 2), Array(11, 2), Array(12, 2), Array(13, 2), Array(14, 2), Array(15, 2), Array( _
16, 2), Array(17, 2), Array(18, 2), Array(19, 2), Array(20, 2), Array(21, 2), Array(22, 2), _
Array(23, 2), Array(24, 2), Array(25, 2), Array(26, 2), Array(27, 2), Array(28, 2), Array( _
29, 2), Array(30, 2), Array(31, 2), Array(32, 2), Array(33, 2), Array(34, 2), Array(35, 2), _
Array(36, 2), Array(37, 2), Array(38, 2), Array(39, 2), Array(40, 2), Array(41, 2), Array( _
42, 2), Array(43, 2), Array(44, 2), Array(45, 2), Array(46, 2), Array(47, 2)), _
TrailingMinusNumbers:=True
Close #1
Nofile:
End Function
Sub caller_id()
Dim caller_id As String
Dim parent_id, child_id As Long
Dim parent As Range
Dim LastRow, r, x As Long
LastRow = Range("A1").End(xlDown).Row
Columns("AF:AF").NumberFormat = "#"
For r = 2 To LastRow
If Range("AF" & r).Value <> "" And Range("C" & r) <> "0" Then
caller_id = Range("AF" & r).Value
child_id = Range("C" & r).Value
Set parent = Range("B:B").Find(child_id)
If parent Is Nothing Then
Else
x = parent.Row
Range("AF" & x).Value = caller_id
End If
End If
Next r
End Sub
Private Sub Workbook_Open()
Dim y As Integer
y = txtimport
If y = 0 Then
Call caller_id
End If
End Sub