Assign primary supplier?

Hi, I've just removed en masse a primary supplier that was attached to every item in my test database hoping that the single remaining supplier for each item would default to being the primary. Unfortunately, that wasn't the case and I'm wondering if anyone can help with putting a statement together that will turn on the tick box for primary supplier on the Supplier tab within Item properties. I'm having trouble finding anything relating to primary supplier in the actual tables. Thanks.