Add a New Contact????
In the meantime, you can access contacts by clicking on the icon on the upper right side (small icon made up of a rectangle with three small stacked squares). This will open Contacts in a new tab of your browser in the Classic Mail look. You can also access your contacts via https://contacts.yahoo.com.
Neither of these suggestions works. there appears to be no way to add a new contact. Please go back to the old Yahoo Mail until this is fixed.
Please refer to this help article on how to add a contact: https://help.yahoo.com/kb/SLN28059.html