If you’re importing a text file, review the field labels.
If the first card contains headers, make sure the headers are correctly labeled or marked “Do not import.” Any changes you make to this card are made to all cards in the file. To not import the headers card, select “Ignore first card.”
To change a label, click the arrows next to the label and choose a new label. If you don’t want to import a field, choose “Do not import.”
When you import contacts from an Exchange account, information that isn’t supported is added to the Note field. Custom fields aren’t imported.
During the import, Contacts indicates if it found duplicates of existing cards, so you can Add contacts from iCloud, Google, and more to Contacts on Mac