You can set a Minimum Order Quantity by using the Update Products via CSV function. Follow the instructions here to update your products via CSV, and be sure to select the 'Minimum Order Quantity' attribute before downloading the CSV template. Download the template and fill out the MOQs for the necessary products. Save changes to the CSV and re-upload. To enable this on your B2B Store, go to your B2B Settings page and then check the ’Require SKU Minimum Order Quantity (MOQ) on B2B Sales Orders’ option.