Code Conversion & Debugging for My App

I need my APK app, which is currently designed for both Android and iOS, to be transformed into a source code and debugged. The app has several issues that need fixing.

The issues I'm experiencing include:
- Crashes and errors
- Performance problems
- UI/UX issues

Since I do not have the original source code for the app, I require a professional who can convert my APK to source code, identify and fix these issues.

Ideal Skills:
- Android and iOS app development
- Debugging and performance optimization
- UI/UX design and enhancement
- APK to source code conversion

Experience with similar projects is preferred. Please provide a detailed proposal including your plan to tackle this project.