Export/Import custom entity

Problem/Motivation

Add custom entity files structure before export

Steps to reproduce

I have installed a theme in my drupal that adds its own content blocks (Modal, Counter, Slider, Tabs, etc.) almost all of them have a field type called hs_settings. When I do the export it tells me that it is not going to export it.

In the documentation I see the code but I don't know how to implement it in my installation

https://www.drupal.org/docs/contributed-modules/single-content-sync/exporting-and-importing-custom-entities-and-field-types →
The documentation explains what we should do to export/import our own content blocks but I don't understand where I should create those files to include that code. Should I create a module that inherits from Content Single Sync or add files to the module? In that case, what would be the folder structure, file extension, etc.

Thank you