Solve a problem in PHP code and make it work in iPhone and Android app

*Please read project description carefully before bidding* Hello Freelancers, 1. I will give the backend files, upload it to my VPS and connect it in both the apps. Make sure it is working. 2. I have facebook code for login and other things but I don't have the account's password. So. I will give another facebook account just change the account id in the apps. 3. Solve this problem:- I already have a completely developed Android and iPhone application. I want an issue to be solved in both the apps. -> This app uses Facebook login. When a user signs up in the app everything is working well. But this same user logs in with this same facebook account in another phone(android or iPhone) then this account is created as new one. Like, suppose if X is the user and X logs in Phone A it's all good and when X logs in with Phone B then this is created as a new user in the database. So the problem here is if the user changes his profile picture, name, age, phone number etc in Phone A then it is not reflecting in Phone B and vice versa. The problem is clearly explained here. Please bid only you think you can complete this project. There are two more minor changes which are very easy for the one who can solve the above problem. Problem:- The app has guest user which is like no login required but it stores the user information in the server(PHP code) and it remembers the phone with a unique id. I think this is making the app to create duplicate facebook accounts in the database. Skills required to apply for the project:- VPS knowledge must, Swift, Android, PHP, Facebook Login integration. Thank you.