Q.How do I deal with mildew on my forget-me-nots?
i planted just 10 seeds in a hanging basket and there is now a lot of thick foliage but also mildew on a lot of leaves.

Certified GKH Gardening Expert
I'm including links for three articles to help you with this. You'll need to make sure your plants are not sitting in soil that's too wet, that they have good air circulation. You will need to use a fungicide; the last of these articles will tell you how to make your own at home:
https://www.gardeningknowhow.com/ornamental/flowers/forget-me-nots/problems-with-forget-me-nots.htm
https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm
https://www.gardeningknowhow.com/garden-how-to/info/homemade-fungicide.htm