How to get villagers to like me again after killing their livestock?

Leave the area for 3 ingame days. If you return, people will like you again.

Equally, find a guard and sheath your weapon. Then go to prison or pay your bounty.

Get away from the place, into the wilderness, and wait 3 days before returning.

Well how many people saw? If the whole village saw, yield to the guards. If only a few people saw kill them and your bounty is gone. For example when I killed the last witness of my crime (I attacked Thalmor and farmers), a bounty worth 4000 was removed from Whiterun.

Alternatively, if you're playing on PC; look up codes to remove bounty. Also you could just kill everyone in the village. Unless some are essential, but there shouldn't be any if you finished the main quest.