You can add a new contact to an existing address book by either adding the contact manually or by importing contacts from an Excel or CSV file.
Importing contacts is a good option when you have several contacts to add.
Add a new contact manually
Select Contacts from the navigation bar in order to display your address books. Tick an address book and then click on the Add contacts icon alongside it.
You'll be asked how you want to add your contacts. Select Add an individual contact.
You're then prompted to add the email address for the new contact.
When ready, click Continue.
You can then complete additional information about this particular contact. When ready, click on Save to complete adding your new contact to the address book.