How to Return AT&T Modem?

We cancelled our internet service and Gerald the AT&T csr told me that I needed to return the router to AT&T. He stated that the instructions were easy to find on the internet. Well, I searched the internet and received tons of different opinions, advice, people complaining about being charged for unreturned equipment, other stating that they needed to print out a smart label, etc. I'd rather get an official response since I have received nothing official via email. My cancellation confirmation number is"[edited for privacy-please do not post personal or unique information such as but not limited to full names, employee ID numbers, email addresses, phone numbers, account numbers, etc.]."

Please advise,

Just an average working class Joe...