Well, depends on the quality but some koi, especially bigger, are worth a lot of money. Put an ad in your local paper and sell them. You can also donate them but not too many people can handle that many...unless they’re tiny. If you’re close to Ohio...you can call Ohio Fish Rescue, they can probably take all of them.
The problem is, it’s winter so there’s not too many people looking to get koi. You should wait until spring and you’ll have no issue getting rid of them all. If it’s very cold where you live, you don’t even have to feed them over winter so there’s not much work leaving them there so long as the filter works