How do I sell back my apple iPad mini back?

If you are asking about the Apple Trade In program, go here and follow the instructions to see what your iPad is worth.

Apple Trade In - Apple

If you have an iPad Mini 2, my guess is that Apple will only recycle it for you. It does not have my real value.

Apple Store Returns & Refunds. Click here to read --> Returns & Refunds - Shopping Help - Apple - For the USA "You have 14 calendar days to return an item from the date you received it." The return terms may be different in some countries (the link I provide should open to a page for the country to which your account is set).

- "You can always return the item to any U.S. Apple Store. An Apple Specialist will assist you with your return. Your refund will be processed at that time"