I hate to say it, but indeed your best bet may be to start over, unless those are special seeds that you just can't bear to waste.

Read the link in my sig for some background that will make other advice make more sense, but the basic idea is to make transplanting as stress free as possible. Then, you can take advantage of each transplant to put the plant in fresh, light soil that is correct for the life stage it is about to enter. In the end, you actually BENEFIT from frequent transplants, even though it might seem counterintuitive.
Stressed plants sometimes stay runty for their whole lives so if those were just bagseeds, or a test you were doing, pop a couple more and start fresh.
I like this one soil called Farfards seedling starting mix a LOT. It is ideal for cannabis seedlings.
If you have to save those plants, you will need to flush the pot out a lot- BUT!- since the pot is so large, flushing is a pain: The roots aren't really all that well developed, and the soil that the roots aren't getting into will just sit there sodden for a while and can cause more problems. If you must flush, add MORE drain holes in the SIDES of the pots so it dries out faster.