Hit them babies with some Bacillus Subtilis like Serenade Garden to stop that damping off/botrytis, or copper sulfate or really any biofungicide. I have had ok luck with my PureCrop1 fighting it off but I decided to say fuck it and use Serenade on my seedlings from now on, it works great from what I can tell so far.
https://www.planetnatural.com/product/serenade-garden-disease-control/
That’s the consumer version of this big dog for organic farmers: