Nutrient burn is the over-fertilization or overfeeding of nutrients to your plants. When you supply your plants with their required nutrient in excess, they tend to absorb all of them thus resulting in nutrient burn.
The best thing to save your plant is to prevent nutrient burns from happening in the first place. Do all you can to reduce the chances of nutrient burn from occurring. The excess nutrient can be catastrophic to your plants if not detected on time.