You need to requery the combo box
Where you issue that command is up to you.
The easiest, and arguably simplist is to put a command button on the form which when pressed rins that code.
The neatest is to do it automatically from the Customer form. That requires you to check if the other form is open and if so update the combo using
you probably need wrap that code with an error handler, at the very least on error resume next to cater for the user entering cistomer data without the other form being open. You probably should requery after every insert in the customer form as you cannot guarantee how a user works with the customer form.
Depends on your skill set. Personally i tend to use the simple press button to update approach as it makes each form standalone. Its easy enough to do it automatically but in my books it makes forms overly interdependent and can also be easier break.
I'd rather be riding on the Tiger 800 or the Norton