You have three options when it comes to using or adding an additional key.

• First option is to update your SSH local config file to include any additional keys with an updated IdentifyFile of /path/to/private.key
   
• Second, is to specify the identify file to use for that one connection.
  
  Example: ssh -i /path/to/private.key
   
• Third, you can hold this new key open with an agent by adding an identify to ssh-agent. This way when SSH attempts to connect, it will try all keys loading into your agent.
  
  Example: ssh-add /path/to/private.key