var root = ApplicationData.Current.LocalFolder;
logFolder = await root.CreateFolderAsync(LogFolderName, CreationCollisionOption.OpenIfExists);
The location of the MetroLog file is fixed in its source code line 34, if you want to change it, you should go to the source code and change its position. See File access permissions to put the file in the accessible location in UWP app.
Also see this similar thread: Change MetroLog folder and file name in Windows 10 UWP app