I would like to populate the value of a lookup field through a a copy of a field using custom action buttom.

Example.

Form1 have the  fields CustomerID, Product1, Features and several more

The CustomerID field is a number

Form1Report have the same fields and a Custom Action Buttom for copying  fields CustomerID, Product1, Features into Form2

in Form2 I want the CustomerID field to be a Lookup field to a table called customers. So the fields in the customer form can be used in the reports created basis the Form2. 

The question is how to copy the number in CustomerID from Form1 to Form2 so that in Form2 it is a lookup field?

Thanks in advance