Making a XML template dynamic with php/laravel

Question

Hello I want to make the Xml dynamic, with a input form so a user can change it. After that save and make a new VERSION of the xml file. for now I have made a form that adds a new xml element, but i want to change the elements and make a new VERSION!

<?xml version="1.0" encoding="UTF-8"?>
<config version="2.1">

    <general dryMode="true" logLevel="ERROR|WARNING|NOTICE|INFO|DEBUG">

    </general>

    <api

        username="--username--"
        password="--password--"

    />
</config>

Here is my Controller:

public function store(Request $request)
{

    $xml = new \DOMDocument("1.0", "UTF-8");
    $xml->load('editfile.xml');


    $name = $_POST['name'];
    $password = $_POST['password'];


    //info user
    $rootTag = $xml->getElementsByTagName("config")->item(0);

    $infoTag = $xml->createElement("info");
    $nameTag = $xml->createElement("name", $name);
    $passwordTag = $xml->createElement("password", $password);

    $infoTag->appendChild($nameTag);
    $infoTag->appendChild($passwordTag);


    $rootTag->appendChild($infoTag);

    $xml->save('editfile.xml');

this works perfect but I want to be able to edite the exciting elements