Thanks for asking.
You can either add the code in Theme Options panel under X/Pro > Theme Options > CSS or in Child Theme under Appearance > Editor. More information can be found here. https://developer.mozilla.org/en-US/docs/Web/CSS/@font-face/font-display
You can use following resources to download and setup child theme.
Download Child theme from following source: https://theme.co/apex/child-themes
Please take a look at following article to setup child theme: