Hello @jesuistao,
The icon you are referring to comes from the Font Awesome icon class.
To change the right pointing hand icon in the header notice you can paste in the following custom CSS in your Dashboard > Appearance > Customize > Theme Options > Advanced Options > Custom CSS field :
#quick-contact .top-news-title::before {
content: "\f14a";
}
You can replace the content id value with the Font Awesome icon unicode of the icon of your choice. For reference of all Font Awesome icons see this link.
Hope this resolves your issue,
Best Regards !!