The tiff writer should use the default byte order of your system. But you can force it like this:
using (MagickImage image = new MagickImage("input.tiff")) { image.SetDefine(MagickFormat.Tiff, "endian", "lsb"); // PC// or image.SetDefine(MagickFormat.Tiff, "endian", "msb"); // Mac image.Write("output.tiff"); }