Well they do describe how you can do this on an airgapped machine. I also deleted that old key from my github account after doing this.

On Thu, Mar 5, 2020 at 6:58 PM Yardena Cohen <yardenack@gmail.com> wrote:

On Thu, Mar 5, 2020 at 6:54 PM Morgan Allen <morganrallen@gmail.com> wrote:
> private key... private key... private key.. I swear they call it that for a reason but I just cannot put my finger on it.

Yep. After reviewing the whole thing I decided the risk isn't worth
the money and I'm not taking the bait.