Updates to Reactive iOS/ Android Apps

We are a small healthcare start-up based in the UK. We have an iOS and Android App built using
-React native.
-Firebase

The App has been live for 2 years with many thousands of users. We use Firebase as a backend database.

We are looking for a long-term development partner.

The app is currently live on Android and iOS.

1. The Android app needs an API update.
2. The Android app also needs a Billing library update.
3. Update iOS app firmware too.
4. Successfully upload to iOS and Android stores
5. Fix some minor bugs
6. Improve user interface

This will be the first stage, I am looking for more updates later on.