Using multiple SSH keys. – Acquia Support Knowledge Base

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