Main menu (entire header and footer) is usually not a part of the template, but a part of layout (which is a parent of template and usually only one for entire theme).
In other words, this change is not per template but for entire site.
So you can’t do exactly what you want from the Customizer only*, you’d need to edit the theme code for this. Not very complex, but unfortunately I can’t help here until I see the theme code since Venue is a paid theme…
Also, keep in mind that editing theme code will make it more difficult to update your theme to a newer versions.
You may also consider the route suggested by @Dan-From-Ryviu , but I’d rather use “Custom liquid” section to avoid theme code editing. This way your header and footer will be hidden on this page and you’d need to come up with some kind of alternative navigation using other sections available in the theme.
It may be possible to trick the system by “creative” usage of languages/markets, but I’d rather not recommend it.