Compare and merge 2 csv files based on 2 first col

I have 2 csv files I'm asked to merge where the values from the first column match. Both files can have the possibility of having duplicate values, and if they do, a new row should be created to support those values. If no match is found, then print the value no match.

Except for looking for duplicate values, I am using the following code...

Function GetFirstColumnNameFromFile
{
    Param ($CsvFileWithPath)

    $FirstFileFirstColumnTitle = ((Get-Content $CsvFileWithPath -TotalCount 2 | ConvertFrom-Csv).psobject.properties | ForEach-Object {$_.name})[0]
    Write-Output $FirstFileFirstColumnTitle
}

Function CreateMergedFileWithCsv2ColumnOneColumn
{
    Param ($firstColumnFirstFile, $FirstFileFirstColumnTitle, $firstFile, $secondFile, $resultsFile)

    Write-Host "Creating hash table with columns values `"Csv2ColumnOne`" `"Csv2ColumnTwo`" From $secondFile"
    $hashColumnOneColumnTwo2ndFile = @{}
    Import-Csv $secondFile | Where-Object {$firstColumnFirstFile -contains $_.'Csv2ColumnOne'} | ForEach-Object {$hashColumnOneColumnTwo2ndFile[$_.'Csv2ColumnOne'] = $_.Csv2ColumnTwo}
    Write-Host "Complete."

    Write-Host "Creating Merge file with file $firstFile
    and column `"Csv2ColumnTwo`" from file $secondFile"
    Import-Csv $firstFile | Select-Object *, @{n='Csv2ColumnOne'; e={
    if ($hashColumnOneColumnTwo2ndFile.ContainsKey($_.$FirstFileFirstColumnTitle)) {
        $hashColumnOneColumnTwo2ndFile[$_.$FirstFileFirstColumnTitle]
    } Else {
        'Not Found'
    }}} | Export-Csv $resultsFile -NoType -Force
    Write-Host "Complete."
}

Function MatchFirstTwoColumnsTwoFilesAndCombineOtherColumnsOneFile
{
    Param ($firstFile, $secondFile, $resultsFile)

    [string]$FirstFileFirstColumnTitle = GetFirstColumnNameFromFile $firstFile

    $FirstFileFirstColumn = Import-Csv $firstFile | Where-Object {$_.$FirstFileFirstColumnTitle} | Select-Object -ExpandProperty $FirstFileFirstColumnTitle

    CreateMergedFileWithCsv2ColumnOneColumn $FirstFileFirstColumn $FirstFileFirstColumnTitle $firstFile $secondFile $resultsFile
}

Function Main
{
    $firstFile = 'C:\Scripts\Tests\test1.csv'
    $secondFile = 'C:\Scripts\Tests\test2.csv'
    $resultsFile = 'C:\Scripts\Tests\testResults.csv'

    MatchFirstTwoColumnsTwoFilesAndCombineOtherColumnsOneFile $firstFile $secondFile $resultsFile
}

Main

The contents of the first csv file is:

firstName,secondName
1234,Value1
2345,Value1
3456,Value1
4567,Value1
7645,Value3

The contents of the second csv file is:

Csv2ColumnOne,Csv2ColumnTwo,Csv2ColumnThree
1234,abc,Value1
1234,asd,Value1
3456,qwe,Value1
4567,mnb,Value1

The results is:

"firstName","secondName","Csv2ColumnOne"
"1234","Value1","asd"
"2345","Value1","Not Found"
"3456","Value1","qwe"
"4567","Value1","mnb"
"7645","Value3","Not Found"

Since the second file has a duplicate value of 1234 the result file should be:

"firstName","secondName","Csv2ColumnOne"
"1234","Value1","abc"
"1234","Value1","asd"
"2345","Value1","Not Found"
"3456","Value1","qwe"
"4567","Value1","mnb"
"7645","Value3","Not Found"

Is there a way I can do this?