Home button

I’d like to make a home button on the site: http://www.cruddengroup.com
It’s the “Crudden research group” image at the top left of the page a home button; it’s a clickable image at the moment, but takes you to a 404 page.
I didn’t create the site but am maintaining it now, and would like to make it more user friendly. It’s a custom theme, but I don’t see where to change something that’s not directly on either the header or footer menu.
I haven’t had any trouble with basic posts and updates to pages, but am having trouble with the details!
Thank you!