Why is my burger icon not working on my mobile site?

The burger icon has stopped working on my mobile site, and customers can’t navigate the site

I spoke to Shopify support and downloaded a new debut theme to preview the button, which works, on a new theme, however, they said I would have to either rebuild my whole site or amend the code. I do not know anything about code, so need some help

I would need to see the site to comment. May be something interfering or delaying the javascript.