Wash the plant off thoroughly with water to get the weed killer off.  If it hasn’t absorbed too much of the weed killer, then perhaps you’ll only lose the leaves and it will grow new ones to replace what is lost.  if the weed killer was in contact with the leaves too long before it got washed off then you might lose branches and stems and, possibly the entire plant.  Water, water, water…especially to wash the weed killer off the leaves and stems.