Refactoring of a chat module

We use a homemade CRM build upon the MVC framework Codeigniter v3. Technologies involved are Php 7, MySQL, javascript, HTML and CSS. We added an HMVC add-on to structure the code in modules. Currently our application has more than 200 modules and more than 300 database tables. We use GIT in our development process.

Your task is to refactor a chat module. You start by analysing the code of the module to understand how it works. Then we discuss about its architecture. We may decide to change it. Finally you implement the changes and support our team during the deployment process.

The budget is approximate,please leave your reasonable bid!