Throw the seedlings away and start over. Use fresh potting mix. This time, place yellow whitefly sticky traps all around your plant area. The gnats will be attracted to those. Water the new seedlings from the bottom and wait till the surface soil dries a bit before watering again. Air circulation is a must.

Some people use chamomile tea but I've never needed it. Don't use chemicals on tiny seedlings. They can't handle it.

I can't imagine that pyrethrins would hurt seedlings. I have a feeling that your plants are toppling because of fungus gnat damage. Usually they don't hurt plants that much, but serious infestation could damage seedlings. But I suspect your plants toppled over suddenly just because you were weighing them down with the spray, and the soil structure may be such that it is not providing good support for the stems Best way to avoid fungus gnats is to just let the soil surface dry out. Once the seedlings are big enough, the soil surface need not be kept moist.