To tag a group of contacts:
Click “Contacts” in the top menu to navigate to the Contacts Overview.
Click into the search field and then click “Advanced Search” when it appears:
Use the segment builder to find the group of contacts you want to tag. Click “Search.”
Verify that you want to tag all the contacts that appear in the contact list and click “Edit All” to display the Bulk Editor:
Click the “Add a tag” option.
Type the name of the tag you want to apply in the text field that appears:
Click “Add tag” and then click “Apply Changes” to finish the process. Your changes will begin processing immediately in the background.
To learn more about working with tags, see the help article on that topic.