open links in iframe one by one when press button – Blancer.com Tutorials and projects

i’ve a array of three links for a button which i’m using in footer and when i press the button again and again , array will work one by one good ..and every time it shows a link when press the button. That is good.
but i want , when i click on button that “link” should open in “iframe” … i used iframe code to pass them src= button id but not working.. please below code and help..
.
my button code with array

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
.footer {
   position: fixed;
   left: 0;
   bottom: 0;
   width: 100%;
   background-color: red;
   color: white;
   text-align: center;
}
</style>

<script>
let link = new Array()
link[0] = "https://www.clc-uk.org.uk/cms/cms.jsp?menu_id=26131&postcode=AL3+8QE&distance=20"
link[1] = "https://www.clc-uk.org.uk/cms/cms.jsp?menu_id=26131&postcode=AL5+3NG&distance=20"
link[2] = "https://www.clc-uk.org.uk/cms/cms.jsp?menu_id=26131&postcode=AL4+3NS&distance=20"

let intlinkIndex = 0;

function writeLink() {
  if (intlinkIndex >= link.length) {
    let btn = document.getElementById('btn');
    btn.style.display = 'none';
    mylink.style.display = 'none';
  }
    document.getElementById('mylink').innerHTML = '<a href="' + link[intlinkIndex] + '">' + link[intlinkIndex] + '</a>';
    intlinkIndex++;



}
</script>





</head>
<body>



<div class="footer"> 

<button id="btn" onclick="writeLink();">Click Me</button>

<div id="mylink"></div>

<br>


<iframe id="iframe" src="mylink" width="100%" height="400"></iframe>

</div>

</body>
</html>