code: function changeAddrFromMnemonic(walletInfo, index, BITBOX) {
    // root seed buffer
    const rootSeed = BITBOX.Mnemonic.toSeed(walletInfo.mnemonic)
  
    // master HDNode
    if (walletInfo.network === "testnet")
      var masterHDNode = BITBOX.HDNode.fromSeed(rootSeed, "testnet")
    else var masterHDNode = BITBOX.HDNode.fromSeed(rootSeed)
  
    // HDNode of BIP44 account
    const account = BITBOX.HDNode.derivePath(masterHDNode, "m/44'/145'/0'")
  
    // derive the first external change address HDNode which is going to spend utxo
    const change = BITBOX.HDNode.derivePath(account, `0/${index}`)
  
    return change
  }
docs: Generate a change address from a Mnemonic of a private key.