Saving xml files on extern USB-Stick

Hey, this is my first thread in this forum. My history: I just began developing in Xamarin forms. I´ve got a problem: I have a xml file in the following folderpath on my tablet storaged (var backingFile4 = Path.Combine(System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal), "test.xml");.
I have connected the tablet to a USB-Stick and I wanna save the file from my tablet to a path on the stick. Would you please post a little snippet for my understanding?
Please help... LG Andre