Power off your iPhone.
Locate the SIM tray on the side of your iPhone.
Insert the SIM eject tool (or a paperclip) into the small hole next to the tray.
Press to eject the SIM tray.
Pull the SIM tray out.
Remove the SIM card from the tray.
Reinsert the SIM card into the tray in the correct orientation.
Push the SIM tray back into the iPhone until it clicks into place.
Power on your iPhone.