There's a small hole in the SIM card tray. Push either a SIM card eject tool or a paperclip into it.
Press the tool in order to eject the tray. You may need to use some force to do this.
Take the SIM card tray assembly out of the iPhone.
Make sure that the SIM card is in proper orientation (in relation to the tray) when you're placing the SIM card back.
Lift the button assembly cable from its socket on the logic board with a spudger.
Make sure that you lift the connector and not the socket itself. If you lift the socket, you risk breaking the connector completely.
Lift the Lightning connector cable from its socket on the logic board with a spudger.
Make sure that you fold the Lightning connector cable so that it's not in the way of the logic board.
Disconnect the rear-facing camera cable from its socket on the logic board, using the flat end of a spudger.
There are seven screws on the logic board. You need to remove them.
One 2.4 mm Phillips screw
Two 2.3 mm Phillips screws
Four 2.8 mm Phillips screws
Remove all of these with a small flathead screwdriver.
Lift the logic board up so that you can grab it with your fingers. Do this with a plastic opening tool.