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
In this function you have an $args array ( in 2 places) :  . In both places  replace   ‘orderby’         => ‘meta_value’, with   ‘orderby’         => ‘rand’,  .