Single black, lifted & irritated scale?

My brothers corn snake has a single scale that has been black for a long time he said. Recently it looks quite irritated and is lifted up a bit. What could this be and any way to treat it?

Thank you

My brothers corn snake has a single scale that has been black for a long time he said. Recently it looks quite irritated and is lifted up a bit. What could this be and any way to treat it?

Thank you