If you need to create an Enumeration from a String, I wrote an article about this a few months ago.
https://medium.com/mendix/how-to-create-an-enumeration-from-a-string-in-mendix-ec1c410e0c60
If you just want to set the value of the object member to a specific value that exists in your enum Create_Cost_List.ENUM_PC, then the correct way to express it is using
Create_Cost_List.ENUM_PC.PC
If that's not what you're looking for, could you please clarify further what you are trying to achieve?