How to use FBDI Upload Customers for adding dunning purpose

Summary:

We want to use the Oracle Dunning Process however there does not seem to be an easy way to update customer data so that

1) We can update a bill to site (the primary one) to then also have a dunning purpose so that the customer can be used for Dunning Letters.

2) Mass updating existing contacts that have a Bill to responsibility type to also add Dunning responsibility type.

On the simplified Upload Customers template there seems to be lots of required fields. I am unsure how I can query this data in BI Publisher to get for example *Site Purpose Source Reference?