Blemish are common, to help the horse, you should shower his legs and apply clay and make him walk as much as possible to ease the blood circulation!
Unfortunately a lot of horses have blemish... Especially in equestrian centers where they work a lot not always with all the care needed.
A blemish is a sort of soft (and sometimes hot) bump. It appears when a horse has worked intensely. It is not easy to make them disappear. Shower, clay, good working agenda of course and standing wrap will limit their apparition :)