The answer is you can't remove it.
And the longer it is there, the more problems there will be.
It should be removed under local anaesthetic.
You will have to have one or more x-ray films. The best way to take the films in such a situation is to draw a line with a ball-point pen and tape another needle to the surface of the knee, directly over the line. Then the same is done with another needle on another axis. After the shots are taken the needles on the surface of the skin are removed, but the pen lines remain. When the fil;m is developed this till enable the physician to precisely determine the depth and position of the fragment.
It is possible to take an x-ray without doing this, but an x-ray film involves distortion, and this is the way to establish the exact depth and axis of travel.
It will most likely have to be removed by a doctor or surgeon depending on how deep it is. Good Luck
Please seek emergent care to have it removed.