Their actionable advice is in the sentence before that. You're quoting a supporting motivation and treating it like the thesis.
"getting and applying professional feedback for one's interview skills has a better ROI in my opinion."
And I specifically addressed that: it's difficult to get any actionable interview feedback because companies tend not to supply much (if any) useful interview feedback probably due to legal concerns.
I think he was suggesting getting feedback from doing mock interviews with friends or interview specialists.
For resources of people who might be able to help, I would include people like a mentor, hired professional, or trusted friends who are good communicators.