Example to how change the search string
<?php
add_filter('yith_wcas_search_with_like', '__return_true');
add_filter( 'yith_wcas_search_string_manipulation', 'my_yith_wcas_search_string_manipulation' );
function my_yith_wcas_search_string_manipulation( $string ) {
$string = str_replace( '$', '%', trim( $string ) );
$string = str_replace( '.', '%', trim( $string ) );
return $string;
}