New version with a lot of new functionalities and its documentation is now available on its new repository CreativeBulma - BulmaCollapsible.
The extension comes with a JavaScript implementation to expand / collapse accordion items. Don't forget to include it in your project.
<script type="text/javascript" src="/node_modules/bulma-accordion/dist/js/bulma-accordion.min.js"></script>
Then just add the following code once your DOM's ready:
var accordions = bulmaAccordion.attach(); // accordions now contains an array of all Accordion instances