To get the Sie sind das Essen und wir sind die Jaeger! achievement in State of Decay 2 do the following:
When you're in the game press Up on the D-Pad, then from the menu that appears select Ask for Help or Volunteer to Help. Either will net the achievement. You can cancel matchmaking right after if you don't actually want to play in multiplayer, as that's what the flare is for.
To unlock a corresponding achievement, follow this guide as well: