Split the PDF

At the moment both PDF’s have to be created, so you will have to simply tell them to ignore the normal label and use the return label.

yes, i automatically send the customer the pdf with the labels. However, I only need the second page of the PDF for the return label

You would have to use a PDF library to do that, the plugin creates both labels.

the plugin creates a pdf with both labels as content. I would like to see the pdf created by the dhl plugin in two pdfs so that I can only send the return label

 $attachments = $upload_dir['basedir'] . '/woocommerce_dhl_label/dhl-label-'.$order_id.'.pdf';
    wp_mail( $to, $subject, $message, $headers, $attachments );

that works great so far. However, I only need the second page of the pdf with the returned content

Unfortunately, the return label is embedded within the response of the normal label so it cannot be separated, unless you use an external library to do so.

Where can I find the creation of the PDF in the plugin? There you should be able to specify what should be generated

The label is created on the DHL end not on WooCommerce, and then both are returned together.

I was able to solve the problem with a self-written plugin.