First make sure you've wrapped up that outlaw biker mission and cleared all the hordes to get 100% on the horde killer storyline, since that's what unlocks the reset feature. Once you've got those done, just pop into your options menu and look for reset jobs, where you can choose to bring those hordes back whenever you want.

Something cool to know, you can actually do the same thing with those ambush camps and infestation zones if you've completely finished their storylines too. The best part is, there's no limit to how many times you can reset these challenges, which is perfect if you want to try out different strategies or just enjoy taking down massive freaker hordes with different weapons and tactics.

Just remember, you'll need to load up your completed save file first, and make sure you've actually finished the main story before any of this becomes available. Pretty nice way to keep the action going even after you've technically beaten everything.