Update a form (or table) from another form.

[Tariq New 2 Access]

Hi!
I have been reading some threads but I could not find what i was looking for.
I want to update a form (or table) from another form. I have very little
experince in Ms Access and I need help.

I have two tables

Table 1 - Customer_Details
CustomerId - Primary Key
AmountDue - This is the total amount due (I've eliminated the other fields)



Table 2 - Credit_Sales
SalesId - Primary Key for this table
CustomerId - Refers to my customer
ThisSale - The sale I have made today


My first table already has values in that.
E.g In Table 1 - Customer_Details
CustomerId AmountDue
ABC123 $250.00
CDE125 $300.00

Each time my customer purchases something, I will record the value in the
Field (ThisSale) together with his CustomerId.

When I type the following data in the Form for Credit_Sales
E.g
SalesId - Mar1234
CustomerID - CDE125
ThisSale - $ 59.99

This should update Table 1(Customer_Details) to
CustomerId AmountDue
ABC123 $250.00
CDE125 $359.99

I have a "Save Record" Command Button on my Credit_Sales form. What I want
is that, when I click on the "Save Record" Command Button, the value in
[Credit_Sales].[ThisSale] is automatically added to [Customer_Details].
[AmountDue] as given in the example above.

Could you please help me out. Any help you can provide here would be greatly
helpful.

Thanks in advance.