I need some help.

I need to show value in dropdown on load of a subform during the edit of a record.

I have a form and a subform. In subform, I have created a dropdown in which I am displaying product name from view. 

When I Click on the add new button on subform, dropdown is displaying all the product name. 

When I save the form its information are getting saved in the view. 

But When I edit the same record, then value which was selected previously from dropdown is displaying, but when I want to select another value from dropdown then in dropdown it doesn't show all the products.It only show product which I selected previously.

Please tell me how can I show all dropdown value in subform.