Insert a SIM card eject tool or a paperclip into the small hole in the SIM card tray.

Press to eject the tray.

This may require a significant amount of force. However, ensure the eject tool is properly aligned beforehand as to not damage the eject mechanism inside the phone.

Remove the SIM card tray assembly from the iPhone.

When reinserting the SIM card, ensure that it is in the proper orientation relative to the tray.