As everyone has said more than once you don't and shouldn't store this.
You can calculate and display it at any stage in your operation, and if any of those fields get changed you don't have to worry about trying to update the stored value.
So in your forms Underlying query
Code:
codigoRFQ : Format([YourDate],"yyyymmdd") & "-" & [Factory_Code] & "-" & [ID_Item]
Or on an unbound text control on your form in the Control Source
Code:
= Format([YourDate],"yyyymmdd") & "-" & [Factory_Code] & "-" & [ID_Item]