The client has a way to specify what server to use. That is described at the bottom of this file: https://github.com/Librum-Reader/Librum-Server/blob/main/sel...

It will be in the Server’s readme very soon.

Haven't tried to install it myself but was looking through the git repo for this exact info. Just do it like every other project, either let the user configure it in the frontend through config or make it an environment variable.