Apologies if my question is hard to understand - I'm unsure of the proper terminology to use.
What I want to do is the following...
As an example, I have a list called "Sales" that contains a column called "Customer". "Customer" is populated as a lookup from a list called "customerList". The user selects the customer from the drop-down when completing the Sales form.
However, sometimes the customer will not be in the list and needs to be added, so there is another field in the form called "New Customer". When the form is submitted a workflow adds the new customer to customerList so that it is then available for future users to select.
How can I do this AND update the Sales list record that has just been submitted so that the new customer is added to the Customer field as well as the New Customer field?
I hope that makes sense!