Use a paper clip or SIM tool to remove your physical SIM card. The Trade-In Process
The Apple Trade In program allows you to exchange your current iPhone for credit toward a new purchase or an Apple Gift Card. If your device has no trade-in value, Apple will recycle it for free.
Go to Settings > General > Transfer or Reset iPhone > Erase All Content and Settings .
Once Apple receives and inspects the device, they will finalize your credit. If the condition differs from your description, they may offer a revised value, which you can accept or reject.
Use iCloud Backup (Settings > [Name] > iCloud > iCloud Backup) or connect to a computer to save your information.
This is critical; Apple cannot accept devices with Activation Lock enabled.