Super easy method! The xbox app allows you to open up multiple instances of Among us. We can use that to our advantage with this achievement:
First open 7 instances of among us.
Second host a game and set imposters to 3, kill timer to 10 then join with every tab of among us on local. And third set the map to whichever map you're wanting to get the three wins on. Start the game. Find your imposter tabs and kill the crew-mates fast. You should unlock this achievement straight off since you have 3 imposters on your account causing three wins. Hope this helps!