I learned how accidentally. Trying to stay awake on long car drives and noticed that when I forced my eyes wide open my ears moved little bit as well.

Repeatedly flexing these eventually developed into more fine control to where I can flex the muscles that waggle the ears without moving the eye muscles. Once you accidentally activate them it gets easier and easier to manually activate them.

I feel the flex from the tip of my eyebrows through the temples to the top connected part of my ears.