Hi there,
You can create a new package to customize the existing functionalities
Please follow the below guide to create
Link: https://devdocs.bagisto.com/1.x/packages/create-package.html
To override the Model: https://devdocs.bagisto.com/1.x/advanced/override-core-model.html
To override controller: https://forums.bagisto.com/topic/320/how-to-override-your-webkul-controllers-repository-and-classes