how to add code to service provider by artisan command

i created an Artisan Command that created Repository. A Repository File and an Interface.
when user run below command, this files will be generated.

php artisan make:repository RepositoryName

now, next step is to add bind code to RepositoryServiceProvider in register method.
How do I add the following code to that file?

$this->app->bind(
    RepositoryNameInterface::class,
    RepositoryName::class,
);

and generally, how to add custom code to the method of class in PHP?