Hello,
Thank you very much for choosing our theme and for contacting us.
You can change the font by means of the Advanced typography option, which allows you to choose the item from a drop-down or insert your custom CSS class. Please navigate to the Theme Settings > Typography > Advanced Typography.
Here is the documentation providing more detailed instructions:
https://xtemos.com/docs/basel/advanced-typography-settings-2/
If you tried and still have difficulties, please provide your site admin access I will help.
Best Regards