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The quick and simple answer is to flush with plain pHed water until your plant recovers.
More info is required if you want a more detailed answer.
What's the pH and ppm of your run off?
Are you growing in soil? coco? hydro? What ppm nutrient solution are you using?
What do your leaves look like? Are they very dark green or ?
If your run off is very high ppm you should definitely flush your medium with plenty of pHed water if the pH of your run off is very acidic you should try to add pH ~8.0(depending on how acidic your medium/run off is) water depending on how severe it is at least that's what I would do. It is safer however more time consuming to correct the pH with pH 7.0 - 7.5 water or dilute nutrient solution.