How to fill form in cgfns when i dont have a surname?

[Mozmoz]

I have been wanting to fill the online application for CGFNS but I am having some difficulties with the procedure. The form requires me to fill my first (given ) name, middle name and last (family/surname) name; the first and last name being mandatory to fill. I am a Tibetan and I don't have a passport like all other Tibetans. For us, we have an "Identity certificate" that works as our travelling document. So in my Identity Certificate my given name is Tenzin Lobsang and the column for surname is left blank because I don't have a surname. So, I am left in confusion as to how i can fill the personal details for the CGFNS application. There must be some way for people with no surname to fill the form. Should I fill my name Tenzin Lobsang in the first (given) name column n fill the last (family/surname) name as N/A? Is that acceptable? Because that matches with my "Identity Certificate" since i dont have a surname or should I fill Tenzin as my first (given) name and Lobsang as my last (family/surname) name which doesn't match with my "Identity Certificate"? Your help and guidance will be much appreciated.