I don’t know how to return my old I phone

As I said, you should have received a box to return it in, as well as a return package address label. If you did not, then you need to contact Apple support and explain to them you did not get a box to return the device in. They should explain what to do.

Return it for what? If you are trying to return for service, or return for a trade-in, you will receive packaging from Apple to do that. If you are referring to something else, then you need to explain clearly.