Pepper seedlings curl for various reasons. The most harmless is the uneven growth of the leaf. Then the central part grows very actively, while the leaf blade does not keep up with such a speed. In this case, no special actions need to be taken.
Another reason is a disease. For example, often it begins due to a lack of potassium, which means that seedlings need top dressing. All plants must be sprinkled with half a glass of ash. Or make top dressing with potassium sulfur by making a solution of 1 tbsp. l 5 liters, applying 0.5 liters per plant.
The last reason is pests. They are visible to the naked eye: yellowness of leaves, cobwebs. It is possible to get rid of aphids, spider mites and other uninvited guests by folk remedies or by applying insecticides.