You would have to make a deal OTC with large holders, merchants, and miners.
I had a dream once that I won the Powerball, $250M USD and market bought every coin on the exchange up to the ATH. Completely effing over the whale bear thats been putting up large walls lately.
He should go slow. Might take months, and for sure would push price up.
Forcefully spend all those millions would be spiting in your own food, since you would push price really high and soon after you will change all money into BTC, price would go on free fall. you would lose lots of wealth this way.
It would take months to buy that much BTC at least slightly normally.