Change default status and replace the icon for an hamburger menu

When the screen becomes too small (i.e. if I restrict the browser window, or if I open my website from mobile) the menu becomes an hamburger (?). I want to know how to do the following two things:

Change the default status of the menu from the “not toggled” status (when you can only see ?) to the “toggled” status (when you can see the whole opened menu, and tapping on ? closes it).

Change the symbol from ? to another, perhaps something like “? MENU” or perhaps an entirely different thing.

How can I do these things? If it helps, I am using the Illustratr theme.

The page I need help with: [log in to see the link]