In short there's no way to recover the passphrase for a pair of SSH keys. Why? Because it was intended this way in the first place for security reasons. The answers the other people gave you are all correct ways to CHANGE the password of your keys, not to recover them. So if you've forgotten your passphrase, the best you can do is create a new pair of SSH keys. Here's how to generate SSH keys and add it to your GitHub account.