Overall your seedling actually looks pretty good. The newest growth is green and healthy. I would definitely leave the plant alone now and give it some time to grow. Generally, you want to avoid anything to stress the plant when it's already experiencing problems, but at this point, you've got a healthy looking growing plant so I think you should be fine.
The initial symptoms with the lower brown spots and curling looked like a
Phosphorus deficiency to me. If you're already using nutrients, I would guess you were seeing those symptoms either from the pH being incorrect or because of root problems, for example overwatering. Have you been checking the pH? The pH being too high or too low is the number one cause of nutrient deficiencies.
How often are you watering the plant and how much are you giving at a time? It's a small plant in a big pot so you want to be careful to avoid drowning it. At this point, I wouldn't soak the whole medium because the plant won't be drinking enough to go through it all. You want to be giving your plants enough water that you're watering every 2-3 days. If it's taking longer than that to dry out, you should give less water at a time, and if it's drying out in just a day you should be giving more water at a time. More on
how to water your seedlings in a big pot.
Right now I would focus on TLC, pH, watering properly, and making sure the environment is good with plenty of light but not too hot. You've got this!