Check if you have existing keys by opening the terminal and entering:
ssh-add -l OR ls -al ~/.ssh and check for any file called (usually) id_rsa or similar
Identify the host you're using your current key for. You probably added this key to, for example your github or gitlab account. We will use this later on.
If you don't have a config file on ~/.ssh folder, you will need to create one. We'll get back to this later.