How to add clb to a new rpk

[SBUN2012]

Hello, trying my hand to add a new unit to the game. the example mod have

Human species clb at their model part and can access the base game library of model.
But when i try to do it

my arrow is gray out and i don't know what to do. looked around online and didn't find any detail guides.
Can some on help?
Thanks

 

[The Mentat]

Did you add the Human_Species.clb to the library of your rpk? rpks can only access files that are added to their content.