From there, right-click any selected contact and choose "Add to Contacts".
You can select all of them by selecting the first one, scrolling to the end of the list, and click the last item.
For more information, see Address lists in Exchange 2016.
These are the address list and GAL procedures that are covered in this topic: After you create or modify GAL, you need to update its membership. It may take several hours for the GAL to be updated.
This will update contact information, pictures, phone numbers, etc. Now you have the most up-to-date information from Active Directory in your local address book. Under Send/Receive Groups, you should see an option to "Download Address Book." Now you will be prompted for a few options, and you can choose to update from the Global Address List (this is how your AD should push out contacts).