.net core DEV required to FIRST TASK document asp.net core application as code overview manual

we have a .net core app that has lost its developer, we need to as task 1 create a developer focussed code manual that orientates screens and code together so it serves as a developers map/manual. My project is for creating a technical overview document for an ASP.NET Core application. The format of the document should be a Word Document and should be in written by a developer for a developer. Each screen in the UI should serve as the section heading that includes an overview of what it does (plain English) and then referneced the codebase areas involved at a top level only. This task is +- 20 hours to start. End result is a) you will be well versed in the app and b) we have a roadmap for any developer who joins team. I will create the initial framework. You will have access to the code of course through devops.
You will need SOLID asp.net core skills AND good business logic/understanding.
You will need to be a methodical/documented technician.

Hope you can help
Thanks