Correction in a webapp alredy running

I am looking for a freelancer to help with correcting a webapp that is already running. I am experiencing issues with the functionality and design of the app. The primary programming languages used are HTML, CSS, JavaScript and PHP. There's a Spotify API too. The urgency level for fixing the issues is low and can be resolved within a month. I need someone who is experienced in both languages and can successfully troubleshoot any issues that arise. Furthermore, they should be able to identify any scalability problems and offer solutions on how to correct them. This project requires precise attention to detail as any mistakes could cause the system to function erratically or worse. I am looking for someone who is patient, creative, and deliver results within the proposed timeline. Thanks for your interest in this project.