sir_isOanswered grow question 3 years ago I've seen numerous guys being told they should flush their plants and most of the time their plants end up worse.
Imo, much better to just actually stabilize the medium and nutrient levels, and with gradual sort of changes (unless it is very severe issues).
In your case, your plant probably needs a shitload of varying nutrients now.
I would be giving it some general feed (though fairly low levels, and gradually, consistently and hopefully it recovers somewhat). Shit like molasses for some general elements, calcium, epsom salts, 1-3-2 NPK. and potentially something specifically for microelements along with watering it regularly, though never really soaking it.