function set_owner( $args ) {

    if( $args[1] == true ) {
        $args[0] = wp_fusion()->crm_base->map_meta_fields( $args[0] );
        $args[1] = false;
    }

    $args[0]['Owner'] = '12345';

    return $args;

}

add_filter( 'wpf_api_add_contact_args', 'set_owner' );