add an id to your article (

let target=document.getElementById('viewvideo'), myiframe=document.createElement('iframe'); myiframe.src='the url i want to display'; target.innerHTML='';/** empty the previous one then set content with current iframe*/ target.appendChild(myiframe);

Of course the string of 'the url i want to display' would be given from the value like an onChange event.

This can be done with JavaScript.

What this script does is call the function submitted when the button is clicked, and this function changes the source of the video.

I am not using <input type="submit"> as this reloads the page and I am not sure how to prevent that.

<script>
function submitted(){
    link = document.getElementById("dynamic_select").value;
  document.getElementById("video").src = "https://www.youtube.com/embed/"+link+"?rel=0&amp;showinfo=0";
}
</script>
<form onsubmit="return false;">

<select id="dynamic_select">
<option value="" selected>Pick a Key and Peele youtube video</option>
<option value="pSDTmJtE-Bc">Little Homie</option>
<option value="Dd7FixvoKBw">Substitute Teacher</option>
<option value="iGAMbNKcN1U">Fronthand Backhand</option>
</select>
<button onclick="submitted()">Submit</button>
</form>

<article>

<iframe id="video" class = "youtube" src="https://www.youtube.com/embed/nlD9JYP8u5E?rel=0&amp;showinfo=0"> 
</iframe>

</article>