After installing the app from Shopify, please follow the below steps to integrate the app into your theme.
Step 1: Enable the app to apply your fonts. Open the app and click the Enable button to enable the app.
Step 2: Select the theme that you want to apply the fonts from the app to and then click on the Apply Now button. The app will show all themes that you installed in your store, you can select the published or draft theme.
Select a theme and click Apply now
By clicking on the Apply Now button, you will be directed to the Theme editor to enable the app embed. Simply click on the Save button.
Note: Please make sure you have done both the above two steps to make the fonts work on your site.