Search matched fields from changed row to other worksheets of the right hand side

[logstarter]

Hi,

I have a excel log book for booking resources with multiple worksheets for each month of the year. Each worksheet has the same templates (same headers).

Like Column A-D is for Book A, E-H is for Book B...etc
and Column A, E will record the user name,
Column B, F will record the contact no...etc.

What I would like to do is to check if there are any duplicate user name and contact no in/after the input row. I think I need to have two for loop to loop through the worksheets and the rows. But I have no idea how to do the searching to match both name and contact no. Would anyone could give some advices, please?

Function checkduplicate (byval target as range) as Boolean
    For i = ActiveSheet.Index To ActiveWorkbook.Worksheets.count
        For j = ChangedCell.Row To 200   'assume max row of the worksheet is 500
            
        Next j
        
    Next i
' if no duplicate
   checkduplicate = false
end function

Thank you.