Macro that will flag a duplicate line.

Here's my code from a more complex version...you can tweek it for your needs...

Public Sub MarkDuplicates()    'ByVal pvQry, ByVal pvDupeFld, ByVal pvMarkFld, Optional ByVal pvFld2Check)
'pvQry = query name
'pvDupeFld   = field with duplicate values
'pvMarkFld    = field to change when duplicate is found
'pvFld2Check = field to check to see if 2nd fld different than the 1st one
Dim vCurrDup, vPrevDup, vKey, vCurrFld, vAddr

on error goto ErrDupe

range("A1").select

   'set the duplicate info to search
pvDupeFld = 3
pvMarkFld = 5
pvFld2Check = 2
        
vPrevDup = "*&%"

While activecell.value <> ""
        vCurrDup = activecell.offset(0,pvDupeFld).value
        vCurrFld = activecell.offset(0,pvFld2Check).value
        vKey =  activecell.offset(0,pvFld2Check).value         
        
        If vCurrDup <> "" Then
                '-----------------------
                'MARK THE DUPES...
                '-----------------------
              If vPrevDup = vCurrDup And vPrevFld = vCurrFld Then         'mark this
                    activecell.offset(0,pvMarkFld).value = "Delete"
              End If
        End If

        vPrevDup = vCurrDup
        vPrevFld = vCurrFld
        
        activecell.offset(1,0).select   'next row
Wend
Exit Sub
ErrDupe:
MsgBox Err.Description, , "MarkDuplicates():" & Err
End Sub