Well we would need to know which tablet you have, to know the actual configuration.
However, in most cases you just need to use your thumb or finger to slide it out. Pressing down lightly as you slide outward.
Unless your is the kind that slides into a slot on the side of the tablet, then you would need to carefully grab it and gently pull it out.
Now if it is smaller than the card that should be in there, this is a tad more tricky. You can gently try and shake the device, with the slot facing downward, to see if you can get it to wiggle/slide itself out.
Also you could, but I would be 'really careful' using them, try to remove it with a pair of tweezers. Again, if trying this, be very careful as you do not want to damage the card...