open sim slot on my ipad

See >>> Remove or switch the SIM card in your iPad - Apple Support

Only WiFi+Cellular models of iPad have a SIM slot - and corresponding internal cellular hardware.

For Cellular models of iPad, the SIM tray eject mechanism can be quite stiff…

Using the SIM-eject tool supplied with the iPad, or an unfolded paperclip, insert the tip into the tiny hole in the edge of the visible SIM tray (do not insert the tool in any other openings - as you will cause serious damage). Apply inward pressure to just the tool - keeping your fingers away from the SIM tray itself; the tray should pop-out.

Is your iPad and WiFi AND cellular data model or a WiFi ONLY model?

The cellular model iPad would have Settings, in the Settings app for Cellular data .