I fell on my knee a week ago and it's now numb from the knee down. so if it's a pinched nerve ho do we fix it?

Numbness: Is not the end of the world, but of course it is not normal. Falling directly on the knee can injury the nerves running below the knee cap as well as a nerve along the inside of the knee. I would not expect the whole leg to be numb below the knee, but more like a patch or isolated area. Nerves heal, but it takes time. As long as there is no weakness or instability of the knee, time will heal.