Follow each step carefully.
Press and hold the side button until the power off slider appears. Slide to power off.
Find the SIM tray on the right side of the device.
Use a SIM eject tool or a paperclip to insert into the small hole next to the SIM tray and press until it pops out.
Carefully pull the SIM tray out of the device.
Align the new SIM tray with the slot and gently push it into place until it clicks.
Press and hold the side button until the Apple logo appears.