trade in my iMac

How to prepare your iMac for Apple Trade In - Apple Support:

https://support.apple.com/en-us/HT211120

Look behind the label on the box you received, the return label should be there.

Checked but not there. Apparently, the box was opened and resealed. I will request another box hopefully it will deliver with a full kit.

I also received the box for shipping with no instructions, no label, the upper cardboard or the bag for the power cord.