export facet data

I have a STL file.

I open it to NX and sucessfully got the facet data.

I am done filling the Holes of the facet data.

Now when I export it to IGS or STEP file. The facet data is always missing.

The exported data was always blank.

How to export FACET BODIES to IGS or STEP?

Thanks in advance.

Regards,

~Sen