How do Americans learn to speak Newscaster accent?

Is there a stoah (In Boston or a Store somewhere else) that sells Rosetta Stone for Newscasters. How do I master ESFL, or English as a Second First Language? Right now, I’m stuck somewhere between a Virginia and Boston accent with a liberal smattering of Santa Barbarian and a touch of Minnesotan thrown in for good measure.

Yesterday, @jaytkay posted a link to this quiz that purports to identify where in the USA you came from. I don’t trust it. While it did identify a number of Jellies correct birthplace, it bungled mine terribly. Here’s what it said:

“Your accent is as Philadelphian as a cheesesteak! If you’re not from Philadelphia, then you’re from someplace near there like south Jersey, Baltimore, or Wilmington. if you’ve ever journeyed to some far off place where people don’t know that Philly has an accent, someone may have thought you talked a little weird even though they didn’t have a clue what accent it was they heard.”

Wrong. I was born and reared in Virginia, spent 15 years in California, 3 in Minnesota, back to California, Virginia then Massachusetts 7 years ago. I’ve spent no more than 1 week of my 68 years in Philly. Nothing against the place, but that’s just not where I learned my pronunciations.

But accurate or not, the quiz does make the point that even when most of us think we speak standard American English with no accent, we do have quirky regional ways of pronouncing things. Those who read the national news generally do not. How do I ditch all my quirky pronunciations and adopt Network Standard English?