Send your id_rsa.pub to file /root/.ssh/known_hosts on the server
You can copy the public key into the new machine’s authorized_keys file with the ssh-copy-id command (make sure to replace the example username and IP address below).
From your local machine issue: ssh-copy-id email@example.com
Alternatively, you can paste in the keys using SSH:
cat ~/.ssh/id_rsa.pub | ssh firstname.lastname@example.org "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"