If you order a replacement part from Apple, follow these steps to send back the original part:

Re-package your part in the packaging in which your original part came. Tape the box closed. Remove the pre-applied top label from the box (that’s your copy). Make sure the return shipping label remains on the box. Find the name of the courier on the return shipping label. Visit the courier’s website to schedule a pickup or find a drop-off location. Get a receipt from the courier. In a few days, check that Apple has received your defective part.

Apple is not responsible for any damage during shipping if the package is not properly sealed or is delivered to the courier in poor condition.