Configure public key authentication for new user, when password authentication is disabled

In an EC2 instance, with Amazon Linux AMI, "PasswordAuthentication" is disabled in "sshd_config" file, and "PubkeyAuthentication" is enabled, by default.

Incase "Linux System admin user" creates new Linux user on the EC2 instance, how the new Linux user ssh to the system? Because password authentication is already disabled.

And if the new Linux user generates public key in his local machine, and try to place it, in the EC2 instance, he could not place. Because currently both Public key authentication and password authentication will not work.

How to overcome this scenario?