Custom button to call javascript

I'm trying to create a button that will open a chat window.

These are the instructions Tidio gives but I can't figure out how to do it with a styled button.

https://help.tidio.com/hc/en-us/articles/5464856955932-Opening-the-Chat-Widget-from-a-custom-button-or-a-link#opening-the-chat-widget-with-a-custom-button

I already added the javascript to my site but I'm not sure how to setup the button/link to call it.

If anyone knows how to do it I would appreciate some guidance. Thank you!