You can check this post. It has a screenshot of the header with the info filled in. Just make sure you shift the fields one to the right, that user had placed them in the wrong fields, I think.
Basically antenna #: EML_REACH_RS2 and antenna type: NONE
RS2 got referenced in the IGS database only during 2020 and a recent firmware update should write the info directly to exported RINEX but that might still be in the beta versions and not in the stable ones.