You can add a new public key code example
Example 1: add public key to server
ssh-copy-id -i ~/.ssh/mykey.pub user@host
Example 2: create public key from private
chmod 400 ~/.ssh/id_rsa
ssh-keygen -y -f ~/.ssh/id_rsa > ~/.ssh/id_rsa.pub
ssh-copy-id -i ~/.ssh/mykey.pub user@host
chmod 400 ~/.ssh/id_rsa
ssh-keygen -y -f ~/.ssh/id_rsa > ~/.ssh/id_rsa.pub