Step one: be rich enough to afford to significantly invest in automation. Step Two: Get Richer.

The problem is that to get that initial investment money you need to work, and the jobs that you're doing to earn that money are disappearing due to automation. So you fall one side of the divide or the other - if you're already rich you'll get richer, if you're not rich your opportunities to become rich are disappearing.

You know a huge portion of the American population is living paycheck to paycheck with no savings right? Most people can't "just" buy a robot and magically join the capitalist class.

Doesn't have to be automated, even. Lots of people start out by owning one snowplow. Or one power washer or one lawn mower.