Cold cheese was cut with parev knife - can it be kashered and then used as a parev knife again - if so - how do I kasher it?

If it was soft cheese you do not need to kasher it, you merely need to wash it well so there is no cheese left on the knife. However, if you used the knife for hard cheese such as what is called American cheese or in Israel "yellow cheese", then you must stick the knife in the ground in different places ten times or alternatively use course material such as steel wool to remove any possible fatty residue from the cheese .(חכמת אדם מז:ד) After this is done you may use it normally again for Pareve. Happy Chanuka