Generate private key from a bip-39 seed phrase?

I’m able to generate a new private key and associated public addresses using Bitcoin-core, but what I really want to do is generate a new private key from a 24 word seed phrase. I’m not sure how to go about this and I have not been able to find any examples.

BIP-39 Word list:

https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt

Current code:

var bitcore=require("bitcore-lib");
var buffer=bitcore.crypto.Random.getRandomBuffer(256);
var hash=bitcore.crypto.Hash.sha256(buffer);
var bn=bitcore.crypto.BN.fromBuffer(hash);
var pk=new bitcore.PrivateKey(bn).toWIF();
var address=new bitcore.PrivateKey(bn).toAddress()+'';

If I understand correctly I will generate a hash from 24 randomly selected words (from the BIP-39 word list) then use that to generate a private key. What are the steps and format for hashing the seed phrase?