You do this by completing the quest Oh My Papa. In this quest, your goal is to ally the Great Khans with the NCR. You can ask him to stop the violence against the NCR, and you will complete the quest. One of the options is a favor from the King.
At the end of the quest, you can choose your reward. Blues quest, you can talk to the King and start it.
There are many different ways to complete this quest: If you haven’t yet done the G.I. The NCR is having problems with the Kings, a gang in Freeside. The Volare! quest will make the Boomers pledge their support for you.
The NCR, like the other New Vegas factions, wants the Boomers on their side. He will give you the next quest in the chain. Go there and speak to Ambassador Crocker. When you get to the Strip, you will come across an NCR soldier who gives you a note telling you to go to the NCR Embassy. In continuing helping you guys out, here’s the NCR Quest guide provided by wikicheats.
