Flutter Application UI should be changed

My goal is to modify the user interface of a Flutter application, taking into account both Android and iOS platforms. I require both design and coding modifications; I'll need an experienced UI designer and technologist who can create an app that not only looks and works great, but also meets all of my requirements. I have a reference application or design to present, so the ideal candidate will be able to utilize what I have in mind to create a fantastic new user experience.