Social links in menu bar in twenty fourteen

Hi. On the left site of the menu bar of the website https://www.beveiligingnieuws.nl there are icons that link to social media. Strange is that I can’t find them in the menu in the backend. I can only see the links that are displayed in text on the right site of the bar.
I want to change the links of the icons, but I have no idea how to do that. The builder of the website is unfortunately dead and he left no documentation. I hope somebody knows the answer. Thanks.