Using VBA to search for a matching value on another sheet when a row is added

Hi crystalhowat, this is probably too late to help you but I've posted this in case it is of use to others following.  I made some changes so that it works for me.  tt is the subscript for the transaction file and mm is the subscript for the master file.  I read each row in the transaction file and search for a match on the master then update the master.  The code below is only sample code not my full processing.

Sub FindValues()

Dim lookUpSheet As Worksheet, updateSheet As Worksheet
Dim valueToSearch As String
Dim tt As Integer, mm As Integer
Dim newstock As Integer
Dim instock As Integer

Set lookUpSheet = Worksheets("From LinkedIn")
Set updateSheet = Worksheets("Contacts_Reformatted")

'get the number of the last row with data in Contacts_Reformatted and in From LinkedIn
    lastRowLookup = lookUpSheet.Cells(Rows.Count, "A").End(xlUp).Row
    lastRowUpdate = updateSheet.Cells(Rows.Count, "A").End(xlUp).Row
    
'for every value in column A of From LinkedIn
    For tt = 1 To lastRowLookup
         valueToSearch = lookUpSheet.Cells(tt, 3)
         'look for the value in column D of Contacts_Reformatted
         For mm = 2 To lastRowUpdate
            'if found a match, copy column B value to sheet1 and proceed to the next value
            If updateSheet.Cells(mm, 4) = valueToSearch Then
    '            Set newstock = lookUpSheet.Cells(mm, 8)
    '            Set instock = updateSheet.Cells(tt, 12)
    '            updateSheet.Cells(tt, 12).Value = newstock + instock
                updateSheet.Cells(mm, 29).Value = "IRATA"
                Exit For
            End If
         Next mm
    Next tt

End Sub