Fix Android Mobile App

I am looking for a developer that can apply fixes and enhancements to an android mobile app I have built.
Requirements are:
- You should speak fluent English
- You need to show sample of mobile app you have built in the past
- You need to be responsive in communicating
- You need to be able to deliver changes on time

In your bid, please tell me what you will require (as in the code base, logins, etc)