Good Morning, 

Thanks for your question. 

There is no treatment capable of healing the leaves, but the cause is likely powdery mildew. In sedum and other succulents, powdery mildew fungi tend to cause this type of leaf scarring, rather than creating the prominent white-gray powdery leaf coating. Fungicide can't cure existing infections, nor would it be recommended even as a preventative in this case (if there were healthy leaves to protect), since they may risk harm to pollinators, and Sedum blooms are popular with bees, butterflies, moths, and other pollinators.

Fortunately, the plant usually only suffers cosmetic damage and isn't affected in terms of long-term health. The Sedum should produce new leaves normally next spring after dying back this autumn/winter. You can remove that debris at the end of the season and dispose of it (don't compost unless your compost pile gets hot) so infectious spores are less likely to overwinter around the base of the plant. Even so, plant disease spread and severity is usually tied to weather, so spores could blow back in at some point in another year, as powdery mildew fungi are commonplace. Infections for this fungus tend to occur during periods of moderate to high humidity with warm days and cooler nights, which is why it's most often seen in late spring and fall.

Water your plants at the base, not the foliage. Do not allow sprinklers to spray water on them and ensure they have good air movement around them. 

Here is a link about powdery mildew: https://extension.umn.edu/plant-diseases/powdery-mildew-flower-garden

Good Luck!