I left a piece of cold chicken on a porcelain dairy plate. What must/can be done with the plate?

Shalom, Thank you for your question. Cold food does not transfer taste into other vessels, nor do cold vessels transfer taste into food place on them. That being the case, even though you should not have put a piece of cold meat on a dairy plate, after the fact both the chicken and the plate are still kosher. The meat should be removed from the plate, and the plate cleaned in water that is not hot, to remove any remains of the chicken – it is then totally kosher, and dairy. The chicken may be eaten – however if the plate was unwashed with dairy remains on it, then the meat must be washed before being eaten. Blessings.