You can easily Insert zipcodes in Products (Only for inline form). First, go-to Insert zipcodes at the Insert zipcodes, and select the option
1.Insert zipcodes in products (Only for inline form)=> You select the option Insert zipcodes in products (Only for inline form), and it shows the product list and you can select the product.
2.Save setting=>Note: You should save the setting to apply to the app setting.
Please see the below: