How to use virtual value in stock

Dear support Team

Im Using Dolibarr my issue is I’m purchase 90 KG biscuit in bulk and I Sale in 100 gm packet.

I want to know if I convert biscuit into 100 gm packet then stock virtual value will be decriese and physical value is same

Im unable to find virtual tab in stock menu .

If virtual stock should be enable please guide me how to enable