If this is when you first find the second teleporter stone, have you defeated all the skeletons, etc in that room? Some may wander down into the corridor to the south west.
You should just be able to drag and drop the teleporter stone into your inventory window, or onto the bottom menu interface, to pick it up. Try standing as close as possible.
There is no command to automatically pick it up.
If you drop and use the first teleporter stone (assuming you have it in your inventory), do you teleport close enough to the second to pick it up? If so, you can then use it (without dropping) to get back to the first one.
