recover source C# from executable not obfuscated

I will like to recover the source from an executable (read attached document) the executable is not big and when looking at the executable with DOTPEEK the solution comes round with 90 error on some switch cases on the code. the project is not obfuscated and is not that big. the project is to recover the source from the executable and fix the errors the code might have for compilation and deliver a source code solution that compiles and where that source can be used to edit the winforms on the project and continue de development of the project