Speaking from the experience of a friend, they started out by talking with their manager that they did not want to be a developer in the long term. Shortly thereafter, the manager announced to the team that the developer was going to start taking on project management tasks (like managing the project using Microsoft Project and leading the scrum daily stand ups). They continued in that capacity until they officially became project manager for another team. Now, years later, they are still managing but managing managers and a much larger team overall.