Third-party sidebar (site wide, javascript)

Hello,

I would like to add a sidebar to my website that displays my review score from customers (its from a Dutch e-commerce organization). Sadly, they do not provide a module for Squarespace so I will have to insert the code myself. I do not have any coding experience so I have no idea how to approach this. I have tried it with code injection but it did not show up. Could anyone help me? I am using the Brine theme.

This is the code that is provided to me:

<script>
(function() {
_webwinkelkeur_id = ;
//_webwinkelkeur_sidebar = true;
//_webwinkelkeur_sidebar_position = "left";
//_webwinkelkeur_sidebar_top = "300";
//_webwinkelkeur_mobile = "bottom";
//_webwinkelkeur_tooltip = true;
//_webwinkelkeur_language = ;
//_webwinkelkeur_language_other = false;
var js = document.createElement('script'); js.type = 'text/javascript';
js.async = true; js.src = '//www.webwinkelkeur.nl/js/sidebar.js';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(js, s);
})();
</script>

For webwinkelkeur_id I have to add my own personal code.

Thanks so much!!