Importing user data to exisiting user profiles

I have 400 user profiles on a website.

I need to import phone data and zipcode data to the phone and zip code fields in the user meta.

I can export a CSV file, but I can’t find any way to import a CSV file to add the data in to existing user profiles. I can find plugins which will create new users, but not a plugin which will add data to existing users.

Any help appreciated.