Hello parajk,
Thanks for using Apple Support Communities! We understand you are looking for some information about your trade in device and what to do before sending it back. We are happy to help provide some information.
We have a great guide on what to do prior to selling or trading in your old iPhone in this helpful article:
What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch
Regarding the trade in kit of your iPhone, it should be sent out to you soon after the order is processed in the system. You can take a look at how to track your orders and contacting our sales team in these links:
Viewing & Changing Orders
Contacting Apple
We hope this information helps.
Cheers.