Fix for - pushed to "Completed" instead of "Processing" about wc-donation-platform HOT 2 CLOSED

I found this solution in documentation. Can someone advise me where to insert this code?

add_filter('woocommerce_order_item_needs_processing', '__return_true', 11);

from wc-donation-platform.

Hi,
about your 3 problems:

• autocomplete donations
  The easiest way is to use the plugin Code Snippets: https://wordpress.org/plugins/code-snippets/
• out of date templates
  This is just a warning that the templates have been changed since the fork. If you want to help me there, you can compare the adapted templates with the current WooCommerce template
• order creation failed
  Is it possible that you have created a PDF template (Simple to default/Simple) manually? This template seems to be faulty and prevents the donation from being created. That is why the error message is displayed.

Best regards,
Jonas

from wc-donation-platform.