Hi,
In case if anyone else has same question – as we figured out in private conversation:
Send to admin checkbox in Send additional emails option – sent emails are standard WooCommerce “New order” emails, so you can add/change recipients in “WooCommerce > Settings > Emails > New order > Recipient(s)”.
This is not directly related to the question, but: Send to customer checkbox in Send additional emails option – again sent emails are standard WooCommerce “Processing order” emails, and although recipient is always customer and can’t be changed, you can change other email settings (subject, heading etc.) in “WooCommerce > Settings > Emails > Processing order”.
Hope that helps.