Revision of my android app (solve a few bugs, add in some new features)

I have a Customer relationship management android app (previously developed by 1 of the freelancers here), in which i need to add in some new features and solve a few bugs. I believe it is written in Kotlin, attached below are the interface of my current app. I need to add in a new navigation bar, a few new sections and some admin settings for the app. The data is stored on Firebase, and i also need to add settings to enable me to change database for my different customer database. The current data is very important to me so they must be kept save and would not be affected in anyway with the app revision. Please have a look at the attached photo and the attached excel to have a clear idea of how my app looks and what revision i am looking for. Thank you.