1. Click Inventory
2. Click My Products
3. Click on the Product Name
Once you are in the "Details" tab look for "Quantity"
Minimum quantity per booking
This is a minimum per booking. This means the minimum quantities required for a single booking of this product. Normally, this will be set to 1.
You may need to alter this if you have a product that requires a minimum of 2 units to book, for example a private tour for 2 persons.