First, please check this guide regarding the structure of the theme file and how to customize. The template file responsible for that part is this: wp-content\themes\x\framework\legacy\cranium\headers\views\global\ _brand.php. Copy that file on the same folder on your child theme here: wp-content\themes\x-child\framework\legacy\cranium\headers\views\global. You may need to create the folder that doesn't exist on the child theme. Then edit the file as necessary. The href value is what you need to change.
Hope this helps.