Hi!
Problem solved.
1) Go to dashboard > settings > Google Fonts.
2) Click, “create a new font control.”
3) Name it, “Main Menu” (Name it as you like)
4) Click the “Create Font Control”
5) In the “Add CSS Selectors” box type “.nav-menu”
6) Click “Save Font Control.”
From that moment, you can go to your page and you will be able to use Customize > Typography > Theme Typography and modify the font in “Font family”.
Hope it works!