XML to CSV in C# newbie

Hello Guys i need help with this xml data.

<?xml version="1.0" encoding="utf-8"?>
<xml-data xmlns="http://ift.tt/1Npy4gj">
<form>catalog://Unternehmen/ust/ZM_Formular_online</form>
<instance>

<dataset id="tbl_ZM_tabelle">
  <datarow>
    <element id="knre1">AT</element>
    <element id="knre2">U18713701</element>
    <element id="umsatz_art">0</element>
    <element id="betrag">7605</element>
    <element id="zeile_m">1</element>
  </datarow>

I want to write a csv data by using the knre1,knre2 and "betrag" id's. Its always the same name. It should be looking like this

AT;U18713701;7605

Iam a totally newbie in c# and i need the help.