Fill field based on csv lookup

I am trying to collect customer information and add it to ConstantContact or another e-mail application.  I have created a form with Name, Address, Phone Number, E-mail Address and and a final field based on their Address.  What I would like is for the final field to be automatically populated based on the input above.  I have a csv file with all of the postal addresses and the corresponding data that should be input into the final field.

What is the best way to accomplish this?  I am vaguely aware of Flow and could potentially use it to add the field after the fact.

Thanks,