I hope you are well today and thank you for your question.
Yes to achieve this you have to modify theme code in the Gillion child theme.
Developing custom code for custom functionality is beyond the scope of support that we provide here.
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
There isn’t any document for it but you can find information about child theme in the following page.
The child theme structure is very simple it just contains style.css stylesheet file and functions.php file.