Set up options in dropdownlist from calculated field(array type)

hello everyone,

I have a calculated field "type array"( exemple calcfield=[test1,test2,test3] ).
I want to get values from the calcfield and show it in a dropdown list.
to explain more, I want to add test1, tes2... as a options in the dropdowlist with nintex forms.
Any help please! I am blocked on it from last week 
and the indeed is so urgent.
Many thanks in advance & best regards