So, you first need to determine a list of requests that will be sent to the server, identify the structures of these requests, and understand how the server responds to them. At this stage, you usually have to address the issue of SSL pinning to enable the reading of intercepted requests and responses. Then, you must write the server's code implementation in any programming language that is convenient for you. On the server, you need to implement responses to each request that you listed earlier and manage the storage of player information.
This is the simplest and most logical solution to your question.