Goto project / Settings and edit the configuration. In the server tab you can adjust the port numbers.
[EDIT] This post looks like a similair problem: https://forum.mendix.com/link/questions/92128
Can you open your project in Mendix Studio, the Web Modeler? If so, does it work to start (publish) it from there?
When opening it in Studio, you might get “No branch selected”. In that case you would first have to open it in Studio Pro and set one of your branches to be editable in the Studio, so no you can’t open it.