how to eliminate menu collapse button on website

i have a website im working on at sandyhookfoundation.com/wp…it loads on desktop browsers with a “menu” button in the top left corner of the menu…im sure it for when the window is minimized, or for the mobile version of the site, but i cant seem to find how to eliminate it…i tried inspecting the code, and found the code that generates it, but i cant find the file that the code resides in…any help would be great…thanks