Sent out 12 Units but put 4 since they sold in packs of 3.

I accidentally sent out 12 units but on Amazon central I put four units. I contacted Amazon support and they said that I would have to wait until my product gets finished checking in and then I can contact them back if my available units in my inventory are still not 12. Is there a way I can change my inventory amount? Because they obviously didn’t look inside the boxes to see how many units were In There.