Our “Mission to the United Nations” is to be understood in the sense of “Diplomatic Mission”, i.e. Representation or Embassy, in the framework of the Track II Diplomacy concept that we have adopted (https://en.wikipedia.org/wiki/Track_II_diplomacy).
Diplomatic Representations of countries are called “Embassies” in the “real countries”, but “Missions” in the case of the United Nations, which is not a country. More information: https://www.ungeneva.org/en/permanent-missions
In the same way as for the “real countries”, our activity consists of informing and raising the awareness of the United Nations bodies that can have an influence in matters of autism, and even all of these bodies, since they should all be accessible to autistic people.
To do this, we mainly use this website, and various means (e-mails, letters, meetings, etc.).
We have an address in Geneva for our Mission of Autistan to the United Nations, thanks to another NGO (Franciscans International) which has kindly allowed us to use their address (37-39 rue de Vermont) to contribute to helping the cause of autistic people: 
It is important to note that there is already an autistic organisation in Switzerland, specialising in this activity and in all aspects of relations between the United Nations and autistic people: Autistic Minority International (https://autisticminority.org).
We naturally have a good relationship with them, and – in the same way as with autistic organisations in “real countries” – they have priority, and we have neither the intention nor even the skills to do the excellent work they do. We can only do complementary things, when possible and useful.