You have to go to GitHub and click the fork button, modify the library to do what you want, build the library and use your own modified version.
The library can be found here:
https://github.com/ashishmondal/mondal-ui
Here's instructions on how to fork:
https://help.github.com/en/github/getting-started-with-github/fork-a-repo
After you've modified the library you have three options:
- Build and npm link the build to your own project.
- Rename the npm package, build and publish to your own npm account and then use that new package.
- Test your new features and then open a pull request to contribute to the source project.
Here's a tutorial on npm link:
https://medium.com/dailyjs/how-to-use-npm-link-7375b6219557
Here's the documentation on Angular libraries:
https://angular.io/guide/libraries
Here's the npm documentation on publishing:
https://docs.npmjs.com/packages-and-modules/contributing-packages-to-the-registry
This is how the world of open source works. If there is something you need that is missing, then you help with the project and contribute new features.