Open your index.html file (usually located at public/index.html), add the following snippet to the end of your body tag:
<script type="text/javascript" src="<https://api.linkmole.app/backlinker.v1.js>" defer></script>
It should look something like this:
<!DOCTYPE html>
<html lang="en">
<head><!-- OMITTED FOR CLARITY --></head>
<body>
<noscript>You need to enable JavaScript to run this app.</noscript>
<div id="root"></div>
<script type="text/javascript" src="<https://api.linkmole.app/backlinker.v1.js>" defer></script>
</body>
</html>