I have not received a mailing label with my return and have no clue how to get it back to you

A label should have been included. Contact Apple if one was not:

Refer to this document for ways to contact Apple --> Choose your country or region - Official Apple Support

Select your country (also look for "other" regions), then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.

or:

Contact Apple for support and service by telephone --> Contact Apple for support and service - Apple Support

JH379 wrote:

I haven’t received information on how to send my computer back for a trade-in. I received the box, but no label information.

Look under the label on the return box containing your delivery address.