Selling your old device
When you’re selling an old iOS device, keeping things tidy is of paramount importance. If you plan to use the data on a new device, back it up first. (Ideally, restore it to the new device before you ship the old one, just in case.) Then in Settings on the device you’re selling, tap your name and sign out of iCloud. Then in General > Reset, select Reset All Settings. Once the device has erased everything and reset, shut it down in the usual manner, and remember to remove the SIM.