woocommerce bulk discount

hi
thanks for this plugin.it is working great but just like others i am also facing discount removing problem.In last discussion problem i have seen code but after implement it i got fatal error.
// line 437
public function action_after_calculate( WC_Cart $cart ) {
if ( $this->coupon_check() ) {
return;
}
if ( !$this->bulk_discount_calculated) {
return;
}
if ( sizeof( $cart->cart_contents ) > 0 ) {
foreach ( $cart->cart_contents as $cart_item_key => $values ) {
$_product = $values[‘data’];
if ( get_post_meta( $_product->id, “_bulkdiscount_enabled”, true ) != ” && get_post_meta( $_product->id, “_bulkdiscount_enabled”, true ) !== ‘yes’ ) {
continue;
}
$values[‘data’]->set_price( $this->discount_coeffs[$this->get_actual_id( $_product )][‘orig_price’] );
}
$this->bulk_discount_calculated = false;
}
}
i do not know how to implement this code.
please tell me how to implement it or please update the plugin

https://www.ads-software.com/plugins/woocommerce-bulk-discount/