Change menu button to a custom image

Hi!

If I preview the visualblogger theme, and make the browser smaller the menu button will fold into a small svg icon with three small lines.

I wanted to change this svg image to a custom image I made. I already succesfully identified using the Chrome inspector what I needed to change, and I’ve got the code ready.

The problem is; where do I paste this new custom code? In which file? I plowed through the available files in Tools > Theme File Editor but I can’t find the original code anywhere.

I don’t think it’s the CSS that needs to be replaced because the modified code is going to look like this and contains html:

<button aria-haspopup="true" aria-label="Open menu" class="wp-block-navigation__responsive-container-open " data-micromodal-trigger="modal-7"><img src="https://samplesite.nl/wp-content/uploads/ButtonMenu.jpg"></button>

Hoping you can help me out!