How to add a choir to the music crew of a movie

Hello,

I tried today to add Fiat Cantus, a French choir which is already on imdb (https://www.imdb.com/name/nm10363334/?ref_=fn_al_nm_1) to the crew of an upcoming movie named En Fanfare (https://www.imdb.com/title/tt30327451/fullcredits/?ref_=tt_cl_sm) - we record two days for this project ; but I never find how to add a choir (or an orchestra) to the music department of this movie and didn't find anything about this problem on the help center. Is there any way to do this ?

Merci d'avance !