Olive green cropped button up

Unfortunately the tag only has the size so, I'm not sure what brand this is from! But, it's a very stylish army green button up shirt with a cute french tuck at the bottom. There is a white stain (?) at the bottom right, I'm not sure how it got there when it was hanging in my closet but, if anyone has any ideas of how to get it out let me know!! Never worn before!