First of all please be aware that random order can dramatically increase the page loading time – especially when other database queries are made like in advanced search case. We do not recommend this.
If you want to go further in search_functions3.php file you have function wpestate_arguments_builder http://prntscr.com/oplurg
In this function you have an $args array ( in 2 places) : http://prntscr.com/oplw78 . In both places replace ‘orderby’ => ‘meta_value’, with ‘orderby’ => ‘rand’, .