Link contacts in Contacts on Mac
If you use several accounts in Contacts, you may have multiple cards for a contact—for example, one card from your Yahoo account and one from your Google account. You can link the cards to streamline your list of contacts. The card for each account remains, but Contacts shows just one card with the combined information.
In the Contacts app on your Mac, do any of the following:
Link cards: In the list of contacts, select the cards you want to link, then choose Card > Link Selected Cards.
Unlink cards: In the list of contacts, select the linked card, click Edit, then click the Remove button for one or more accounts.
If you remove an account that contains linked cards, the cards are unlinked and only the cards in that account are removed.