You will have to edit your homepage in Pages section and find the "Page Settings".
Please see the screenshot below.
I also noticed that you only have one menu in Appearance > Menus. Please keep in mind that with one page navigation, you will have two sets of menu. One menu is for your primary or footer menu and the other menu will be used exclusively for the one page navigation menu. Please review how you can set up one page navigation from this knowledge base article.
Hope this helps.