How to get Woodmart search action

Also, how can i get the below code included with ajax search, if possible?

function afas_search_filter( $query ) {
   if ( $query->is_search && ! is_admin() ) {
        $string = strtolower( get_query_var('s') );
	switch ( $string ) {
        case 'nødteppe':
            $string = esc_attr( 'hypotermi' );
            break;
        case 'røksyre':
            $string = esc_attr( 'røyksyre' );
            break;
        default:
            $string = esc_attr( $string );
        }
        $query->set( 's', $string );
    }
}
add_filter( 'pre_get_posts','afas_search_filter', 9 );

function afas_search_function( $search_term ) {
    if ( $search_term ) {
	switch ( $search_term ) {
        case 'hypotermi':
            $search_term = esc_attr( 'nødteppe' );
            break;
        case 'røyksyre':
            $search_term = esc_attr( 'røksyre' );
            break;
        default:
            $search_term = esc_attr( $search_term );
        }
    }
    return $search_term;
}
add_filter( 'get_search_query', 'afas_search_function' );

Or is there another way to set synonyms, replace the search term?
I have used relevanssi before but it is so very slow. The search now is more instant without relevanssi.

Brgds
Rune