ICT6 Project help please!

Hi,
I was wondering if you could give me a little bit of help on my ICT6 project. (AQA)
The Video Rental/Stock system in Access i am creating is coming along good, but i am stuck with a problem. The system is kind of similar to the Video Rental one on the KJS website (Candy Floss). I dont know if this is run by you or not, but any help is appreciated.
The thing is, that when i return a video (a form) back into the database, i would like to add a returned date box on the form which will be later used to calculate overdue books, but also archiving rentals from a rental table, (a copy of past and present rentals), where both tables contain the same fields including the following date fields: loaned, due and returned. The rentals table is where i would like the date returned to end up, in its field for a specific rental. Without this function, the database is 'sort of' incomplete.
But the issue is that the date returned box on the form is unbound, because i do not know how to do this. I am unsure whether or not or how to run a query or macro of some sorts to append the details into the correct field in the correct table for the correct rental.
I am unable to add a text box and select the date returned field from the control source in properties, because it is not there. I think this is because the form is based upon a different table.
If i try to use the Expression Builder, i return to the form with a #Name error in the Date Returned box. Also i have tried to create queries and/or macros for this, but with no success.
Sorry for the long-winded message, but once again any help is appreciated. Included are some screenshots if they are any help.
Thanks in advance,
Nish