With the help of Gecko Customizer settings, you can customize the font used on your site. You can find these settings in WP Admin -> Gecko -> Gecko Customizer -> Site -> Fonts.
Choose the font you want to use on the site from the Google fonts available in the list.
You can also change the font size, line-height and its colors using the settings available in WP Admin -> Gecko -> Gecko Customizer -> Site -> Typography.
Customize global headings and text color: