App testing at publishing to app store and google play

We are in need of testing, bug-fixing and eventually publishing of an app that was developed for us.
The App is called "Dayworker App" and there's already a published version of it on both stores, for testing purposes.

The app is developed with a mix of Javascript and Wordpress and is communicating through json as an app.
The app itself is in javascript and communicates with a wordpress site that it uses for user management and database.

We have all the source files for the app and we need to have it put through x-code and Android studio respectively, for testing and to be compiled and published on our account.

We will provide all the necessary files and login credentials when the terms of the project have been agreed upon.