In a large saucepan, saute the carrots, celery and onion in oil until tender. Add the broth, corn, chicken, parsley, salt, tarragon and pepper. Bring to a boil., Meanwhile, for rivels, place the flour in a bowl; mix in egg with a fork just until blended. Drop dough by teaspoonfuls into boiling soup, stirring constantly. Cook and stir for 1-2 minutes or until rivels are cooked through.