Full stack - Experience Android + PHP + XMPP developer on social network app

I have a social network app that is 2 years out of date. I need you to upgrade and repair to make it work again.

You must be experienced in PHP, XMPP , mySQL, Objective C. Able to manage full stack development.

Some design document is available for your understanding.

Developed in PHP
Native Objective C
GPS
Instant Chat (XMPP)

Facebook Upgrade to see actual info
mySQL DB
Centos Linux backend
Require library upgrade , bugs fixing
Github experience
Testing Library
Behaviour tracking library

Pay attention to UX/UI