I have a spreadsheet of people including zip code, city, and county. Some counties are blank. How do I auto fill the county based on either the zip (first 4 digits of a zip +4 field) or the city? Sometimes we have city and no zip. For only blank fields, can I first check zip field, then use city to auto fill county? I have a master zip code and county reference file.

I understand vlookup can do this, but I'm not a programmer and don't know how to set this up, syntax etc.

Can anyone help?