How do I insert the SIM card into my iPhone?
You will need the SIM ejector tool to remove the SIM tray.
Insert the end of the SIM ejector tool into the hole in the SIM tray. Press firmly and push straight in until the tray pops out. If you don't have a SIM ejector tool, you can use the end of a paper clip.
This is shown step-by-step in the Phone guide > Getting started > Inserting and removing the SIM card