APK Modification & Laravel Integration

I have developed a recharge and bill payment application with a native app APK and an admin panel built using Laravel PHP. I now require some changes to both the frontend and backend of the application. Specifically:

1. Integration of one API into the application.
2. Minor frontend UI changes to improve the user interface.

We have integrated multiple APIs, and we have the option to change APIs in the admin panel. Once we change the APIs from the admin panel (built with Laravel PHP), transactions from the application will work with the selected APIs.

My questions are: The developer provided me with the source code for the web-based admin portal built in PHP Laravel, and he provided the APK file, but he did not give me the source code for the APK. Can we make modifications to the APK?

If yes

I have an APK and a Laravel admin panel for a recharge app. I need a skilled developer to modify the existing APK, integrate a payment gateway API and make some minor UI changes. I require expertise in UI design and API integration, and the ability to work with an APK without its source code.

Ideal Skills:
- APK modification
- Laravel administration
- API integration
- UI/UX design
- Branding and layout design

Key Tasks:
- Modify existing APK
- Integrate payment gateway API
- Change colors and branding in the UI
- Update layout and design elements