How do you open ipad 1 sim slot

You should have a small metal 'sim eject' tool with the iPad :

Open the SIM tray:

1. 1 Insert the tip of the SIM eject tool into the hole on the SIM tray.
   Press firmly and push the tool straight in until the tray pops out. If you don’t have a Sim eject tool, you can use the end of a paper clip.
2. 2 Pull out the SIM tray to install or replace the micro-SIM card.