$ man ssh-copy-id
...
-i identity_file
Use only the key(s) contained in identity_file (rather than looking for identities via ssh-add(1)
or in the default_ID_file). If the filename does not end in .pub this is added. If the filename
is omitted, the default_ID_file is used.
...# man ssh
...
-i identity_file
Selects a file from which the identity (private key) for public key authenti‐
cation is read. The default is ~/.ssh/id_dsa, ~/.ssh/id_ecdsa,
~/.ssh/id_ed25519 and ~/.ssh/id_rsa. Identity files may also be specified on
a per-host basis in the configuration file. It is possible to have multiple
-i options (and multiple identities specified in configuration files). If no
certificates have been explicitly specified by the CertificateFile directive,
ssh will also try to load certificate information from the filename obtained
by appending -cert.pub to identity filenames.