Add this to your child theme’s functions.php:
add_filter( 'wpcfe_print_paper_size', 'custom_paper_size_orientation' );
function custom_paper_size_orientation( $sizes ){
//Change size and orientation of Label
$sizes['label']['size'] = 'A6';
$sizes['label']['orient'] = 'portrait';
$sizes = array(
'label' => array(
'size' => array(0,0,600,841.89),
'orient' => 'portrait'
),);
//Change size and orientation of Invoice
$sizes['invoice']['size'] = 'Letter';
$sizes['invoice']['orient'] = 'portrait';
$sizes = array(
'invoice' => array(
'size' => array(0,0,600,841.89),
'orient' => 'portrait'
),);
//Change size and orientation of BOL
$sizes['bol']['size'] = 'A4';
$sizes['bol']['orient'] = 'portrait';
$sizes = array(
'bol' => array(
'size' => array(0,0,600,841.89),
'orient' => 'portrait'
),);
//Change size and orientation of Waybill
$sizes['waybill']['size'] = 'A4';
$sizes['waybill']['orient'] = 'landscape';
$sizes = array(
'waybill' => array(
'size' => array(0,0,600,841.89),
'orient' => 'portrait'
));
return $sizes;
}