Though last year's entry was McLaren's second Indy 500 attempt with Fernando Alonso, it decided to run its own programme in a loose alliance with Carlin, rather than repeating the partnership it had with Andretti Autosport in 2017.
McLaren and Alonso struggled for pace throughout practice week, and Alonso failed to qualifying for the race when he was bumped from the 33-car field by Juncos Racing's Kyle Kaiser.
Speaking at Autosport International, Brown called that programme a "fiasco" and said he could not hide from the mistakes made in preparation for it, which included a missing steering wheel at McLaren's first test at Texas, and confusion over metric and imperial measurements.
Asked how he has approached his time at McLaren, Brown said: "The owners are awesome, starting with [McLaren shareholder] Mansour Ojjeh, who's a legend in the sport. And yeah, they gave me free rein.
"I'm a big communicator, so I won't surprise them. So with that, I think there's a very high level of trust and so they let me get on with it.
"When we did Indianapolis in 2017 that was pretty crazy idea that I got their support very quickly. And then even after the fiasco last year in 2019, they went, 'You win some you lose some'.
"You can't hide from it. But what you've got to do is learn by your mistakes and definitely not make the second one. Because I would say some of the mistakes I made there were pretty stupid, in hindsight, looking back at what I would have done differently and that's what we're going to do this year, is do things differently.
"But through all that, through the thick and thin, they're outstanding bosses to have and they've kind of given me the mandate [to] get McLaren back to the front."
McLaren has partnered with existing squad Schmidt Peterson Motorsport and will contest a full season as Arrow McLaren SP in the NTT IndyCar Series, the purchase of which was completed by the Penske Corporation earlier this week.
Brown said legendary team boss Roger Penske, who controls his eponymous race outfit and the Penske Corporation, would be "number one on my list as far as a quality individual who empowers his organisation".
"I've been fortunate to have worked with most Formula 1 teams and the IndyCar teams and the Roger Penskes, and I've always said from a very young age, tried to [think], 'What is Roger Penske doing? And what would Roger Penske do?'" said Brown.
"If you kind of keep your eyes open, get some role models and then see what people do, you can learn a lot by those that have gone before you and have been very successful.
"He's used racing to build his business; he's used business to build his racing. I couldn't be a bigger fan of Roger's."