Hey @EmpoweringWomen 

Thank you so much for asking the Klaviyo Community about adding profile properties to existing profiles. Happy to help!

The quickest and easiest way to add profile properties is what you said, uploading a CSV file with the property you want to add, in your case the City where the customer is from. A couple things to remember when checking the formatting of the CSV, the first column must be titled email with their correct email address. Doing so will not duplicate profiles, just add the property that is missing. Next you want to make sure the column for City matches what the existing property title is exactly (i.e. capitalization and spelling) so all profiles contain the same information and not City/city. 

Also check out this other community post about batch updating profile properties. 

Hope this helps get you on the right track! Thank you so much for being part of the Klaviyo Community!

Thank you so much! I went in and added the City, Country and Province in manually...which was really time consuming. I really appreciate this and will do this next time if this ever happens again (which I hope won’t) haha!