I hope you are well today and thank you for your question.
You can use new font on your site using any of the following solutions.
To achieve this, you have to develop custom code in the child theme of Gillion theme.
Developing custom code for custom functionality is beyond the scope of support that we provide here. Please see https://themeforest.net/item/gillion-multiconcept-blogmagazine-theme/19470306/support
If you are not a developer then you can consider hiring a developer to develop it for you. You can hire a developer from any freelance site. Shufflehound recommends the developer https://www.upwork.com/freelancers/~011652ffec8865c6d5