Even if you are on top of ‘earthing-up’ your potatoes there is still a chance of them being effected by a snap frost.
If your potatoes have been blackened by the frost I leave them as they are. I’ve heard of some gardeners cutting the dead foliage off but for me I leave it there using the train of thought that it protects the new shoots if another frost is due.
So for me, I leave the plants to sort themselves out. You will still get a harvest but maybe only 90% rather than if they hadn’t been effected.