If you want to promote a leader in State of Decay 2, you must first turn one of your community members into a hero.
A hero is a community member who has earned a reputation through completing missions helping other communities, and earning a ton of influence.
If you want to get one of your characters to a hero rank, we highly recommend farming and completing every mission that comes up and donating and bringing many items back to your base.
On top of that, killing tons of zombies will also earn both XP and influence that will go to turning one of your community members into a hero.
Eventually, you will be able to promote a leader, provided you completed a lot of missions with one specific character and earned a ton of influence as them.
When this time comes, you will be able to promote them in the community menu, and there will be a bright gold outline of a character in the middle.
Hit space on the keyboard or press A on the controller, or to choose from a list of heroes, choose the one you want, and it will promote that character to a leader in State of Decay 2.
For more on State of Decay 2, check out our other awesome guides!