How do I format/edit/manage an Excel workbook from within a c++/cli app?

Many people will use OpenXML/SDK or other components to works with Microsoft files and thus are not using Office Interop (which I guess you are using even though it is not specified).

Then most peoples would uses C# in such case as it is much easier.

Finally, you won't obtain much help if you don't even show us some of the code you already have.

Find examples in C# and then write equivalent C++CLI code. This is not difficult at all. You replace some dots with :: or -> and write a declaration for each function.

You can also uses some program to convert code between langages but in practice, I find that it is usually best to simply update code manually although it typically works better in the other direction.

Finally, you can always write an assembly in C# too. It will be easier to find samples and easier to write code (for example, C# support default arguments). Usually, if the official documentation don't give sample in C++/CLI, then that technology is less well supported in that language and this might indeed be a case where code would be much verbose in C++/CLI than in C#.