How to copy SSH private key from PC to HA

Anyone knows to which directory on my Pi runnning HA I have to copy a SSH private key from a pc?
It is for controlling my Synology NAS through shell commands.

In the users home directory (login, type „cd“ without arguments and entet). In this directory there should be a .ssh Subdirectory. In that directory put the private keyfile plus the config file.

An other option is to use the -i Option. See ssh -h

When I use Putty and make login to my Pi with username pi and cd to home directory I only see the folders Homeassistant and Pi. I have a ssh (not.ssh) folder in /etc
I only have the id_rsa file, not a config file

I did create the key pairs on another machine and just wants to copy the private key to my Pi so that HA can use it.I did try to create a ssh directory in the Homeassistant directory but when trying to execute this command from putty as user pi I get this error.

ssh -i /home/homeassistant/.homeassistant/ssh/id_rsa -o StrictHostKeyChecking=no [email protected] sudo /sbin/shutdown -h now

Warning: Identity file /home/homeassistant/.homeassistant/ssh/id_rsa not accessible: Permission denied.

I did change the permissions of the ssh directory to 600 with sudo.