How do I send a private embed message to a mentioned user?

I am having trouble with this. If I mention a user in my server, following another command, how can my embed message private message that mentioned user?

For example: =deny (@Mentioned User)

const Discord = require('discord.js');
const client = new Discord.Client();
const prefix = '=';

client.on('message', message => {
  if (message.content.startsWith(`${prefix}deny`) {
    const user = message.mentions.users.first();

    const embed = new MessageEmbed()


client.login('discord token here');