//functions.php file in your theme

//1. First, add a new column "custom". It has to be named : '_custom_key_' followed by whatever your want (no spaces.)
// for exemple : _custom_key_whatever

function my_custom_csv_columns($keys)
{
    $keys[] = '_custom_key_note';
    return $keys;
}

add_filter( 'wqep_included_order_keys_filter', 'my_custom_csv_columns' );

//2. Then, populate the columns with the data you want (for example, several post meta concatenated)
// The first parameter to add_filter must be 'wqep_order' followed by the column key. For this example : 'wqep_order_custom_key_whatever'

add_filter( 'wqep_order_custom_key_note', 'my_custom_key_note', 10, 2 );

function my_custom_key_note($val, $order)
{
    //set $val to whatever you want. $order is a WC_Order object, id is $order->id
        // for example retrieve a post meta of the order

    remove_filter('comments_clauses', array( 'WC_Comments' ,'exclude_order_comments'), 10, 1 );

    $args = array(
        'post_type' => 'shop_order',
        'post_id' => $order->id,
        'type' => 'order_note',
    );

    $notes = get_comments( $args );

    for ($i=0; $i < count($notes) ; $i++) {
        if( preg_match('/AuthNumber=[0-9]{7}/', $notes[$i]->comment_content, $matches ) ){

            return substr( $matches[0], -7 );

        }
    }

    return '';
}