Looking for advice on how to plan a project.

Basically, I need some advice on how to approach a project, in terms of planning out the stories/tasks.

We have a preexisting project that has a backend and frontend. The frontend is served by the backend and we want to break it into two services, one dedicated to frontend and one for backend.

Essentially I have to recreate the current frontend which is just vanilla js, html, css into a new frontend using React. It has to look and function the same.

Any idea how to break this project down into manageable steps? It isn't too complex, but it isn't going to be a walk in the park.