Need Help

I don’t know what’s wrong with my plants I transplanted Three bout a week ago They was perfectly fine til like a week black botched burnt tips cupped leaves , I know I overwatered cause I forgot to water the soil before I transplanted so I watered the plant twice that day cause I wanted to wet the whole pot I had three plants now I’m down to two cause one didn’t make it att all I grow with fox farm soil use nutrients cns17 and cal mag 5 gallon pots and I’m using a wood box I built a work it currently has no ventilation in it my local hydro store say it might be its to hott I use a small fan humidifier cause I read a article there good for veg stage ???? And I’m using a basic grow light these pictures are from the start to now I need help ion tryna have one plant