How to break private method call from a Method Under Test in Microsoft Fakes Unit Testing?

Question

I tried for searching a lot regarding this but did not find any helpful information. And I'm stuck in below situation and seeking for help.

Below is my method which I want to test:

public void MethodToTest()
    {
        this._app = this.GetApp(out this._pId);
    }

//here beelow method which is from the same class and private
private Microsoft.Office.Interop.Word.Application GetApp(out int processId)
    {
        //some code which returns Application

    }

Now I dont want to execute this method instead I want to shim this method using

ShimMyclassName.Allinstances.set_GetAppInt32Out = () => my expected output

But compiler is throwing error:

cannot assign to set_GetAppInt32Out because it's a method group.

So I tried to changed it to:

ShimMyclassName.Allinstances.set_GetAppInt32Out( here it is expecting some out delegate like (OutFunc<WordApplication, int, Microsoft.office.Interop.Word.Application> Value)

In ShimMyClass below is the signature: public void set_GetAppInt32Out(object value);

So I'm stuck here. How can I pass the value and How I can Break the private method call and expect it to return my expected output instead of executing the original private method?