Seems that a lot of people have said something similar, but FWIW…
I’ve been able to move my left eyebrow by itself for as long as I can remember.
I taught myself to move the right eyebrow in 15 minutes standing in front of a mirror. This was about 20 years ago and I can still do it.
For anyone interested, as people have said, it’s about isolating and learning the ‘instruction’ that does it. In this case, seeing as I could raise both eyebrows together, I just did that repeatedly whilst holding the left one in place with my fingers. Fifteen minutes later, and I could do it without needing the fingers.