I need a code to clear the original values for specific references.

I have a many to many relationship between table Products and References by a table called Product_Ref. One Product has many references and one reference can have many products.
and each product has a different price in each reference. (eg. Product1 can be 15.00$ for Reference_Number 101010 but 10.00$ for Reference_Number 030303)
And I want the Price of all the products in one reference to become 0 when a button on a form is clicked.

Please help! Thank you.