Hi,
Please note that any customization would need to be done in a Child Theme form. Editing Theme directly is not good because customizations will be lost as soon as the Theme is updated.
If you need to add a JS, simply go to Appearance > Theme Options > Custom Scripts and you will have two places where the JS can be added.
As far as the menu itself, I can suggest to try something with the jQuery toggle, take a look at this example.
N.B. We have a dedicated support forum available as well.
Thanks,
Emil