LibTiff C# - Setting coordinates

Question

Good day! I am using the LibTiff.NET library to load GeoTiff data in C#. I looked at GDAL, but documentation on c# not good. I read file and coordinates like that LibTiff C# - Getting coordinates then I create new *.tif with similar lat/lon

`

// output.SetField(TiffTag.GPSIFD, modelTiePointTag);

            byte[] temp = modelTiePointTag[1].GetBytes();
            output.SetField(TiffTag.GEOTIFF_MODELTIEPOINTTAG, temp);

`

but it doesn't set

FieldValue[] modelTiePointTagCheck = output.GetField(TiffTag.GEOTIFF_MODELTIEPOINTTAG); // null

what am I doing wrong?