Okay, I was able to Hide a section using this code:
<script>
MsCrmMkt.MsCrmFormLoader.on('afterFormLoad', function(event) {
document.getElementById('postanschrift').style.display= 'none';
});
</script>
WHAT DOES NOT WORK, is if I want a function to be called when I change the dropdown:
<script>
document.getElementById('696494fc-72e0-ea11-a813-000d3a387ed9').onchange = function() {
document.getElementById('postanschrift').style.display= 'block';
}
</script>
Why does the onchange not work?