Sonia
Of course you can export data from redcap into a spreadsheet, do whatever you want in the spreadsheet and import the values back into redcap as long as you have a field for what you want to import in. Eg. CAPTURE ZIP CODE, MATCH TO NAME OF LOCAL.ITY IN SPREADSHEET AND THEN IMPORT THAT VALUE
There are ways to do same as SQL lookups to external database and return values - but this requires some advanced redcap knowledge, SQL skills and possibly admin access so you need help of your admin person - could you give us a detailed example of what you are trying to do.
If you are wanting to only use a valid zip code then you can put the valid codes into a drop down list and search for it by entering the zip code in the search field, if it is not valid it won’t appear in the list
Interested to see what others comment