How can I set up an order form within a Zoho module?

I would like to create a module that allows sales reps to select items and quantities that will be sent as a sample to customers. I have it working so a user can select items from a Multi Select list. But when a user selects an item, it is removed from the list. In other words, you can only select the item one time. How could I make it so the user can select an item and an associated quantity for that item?