For the migration itself I move the projects to SDK style, upgrade or swap the packages, port
ASP.NET MVC or Web API to
ASP.NET Core, and get it building and running with your tests passing. You get the code back as a branch or a pull request with notes on everything I changed. I work in C# every day, mostly on systems exactly like this at a bank. Please send the solution, or at least the list of projects and packages, first so I can tell you what it will take.